diff --git a/Source/diablo.cpp b/Source/diablo.cpp
index b14da41cb..eaa19b552 100644
--- a/Source/diablo.cpp
+++ b/Source/diablo.cpp
@@ -3,6 +3,7 @@
  *
  * Implementation of the main game initialization functions.
  */
+#include <algorithm>
 #include <array>
 #include <cstdint>
 #include <string_view>
@@ -175,6 +176,72 @@ bool was_archives_init = false;
 /** To know if surfaces have been initialized or not */
 bool was_window_init = false;
 bool was_ui_init = false;
+using TickCount = decltype(SDL_GetTicks());
+
+TickCount autoSaveNextTimerDueAt = 0;
+AutoSaveReason pendingAutoSaveReason = AutoSaveReason::None;
+/** Prevent autosave from running immediately after session start before player interaction. */
+bool hasEnteredActiveGameplay = false;
+TickCount autoSaveCooldownUntil = 0;
+TickCount autoSaveCombatCooldownUntil = 0;
+bool wasAutoSaveEnabled = false;
+constexpr TickCount AutoSaveCooldownMilliseconds = 5000;
+constexpr TickCount AutoSaveCombatCooldownMilliseconds = 4000;
+
+bool HaveTicksPassed(TickCount now, TickCount due)
+{
+#ifdef USE_SDL3
+	return now >= due;
+#else
+	return SDL_TICKS_PASSED(now, due);
+#endif
+}
+
+bool HaveTicksPassed(TickCount due)
+{
+	return HaveTicksPassed(SDL_GetTicks(), due);
+}
+
+TickCount GetAutoSaveIntervalMilliseconds()
+{
+	return static_cast<TickCount>(std::max(1, *GetOptions().Gameplay.autoSaveIntervalSeconds)) * 1000;
+}
+
+int GetAutoSavePriority(AutoSaveReason reason)
+{
+	switch (reason) {
+	case AutoSaveReason::BossKill:
+		return 4;
+	case AutoSaveReason::TownEntry:
+		return 3;
+	case AutoSaveReason::UniquePickup:
+		return 2;
+	case AutoSaveReason::Timer:
+		return 1;
+	case AutoSaveReason::None:
+		return 0;
+	}
+
+	return 0;
+}
+
+const char *GetAutoSaveReasonName(AutoSaveReason reason)
+{
+	switch (reason) {
+	case AutoSaveReason::None:
+		return "None";
+	case AutoSaveReason::Timer:
+		return "Timer";
+	case AutoSaveReason::TownEntry:
+		return "TownEntry";
+	case AutoSaveReason::BossKill:
+		return "BossKill";
+	case AutoSaveReason::UniquePickup:
+		return "UniquePickup";
+	}
+
+	return "Unknown";
+}
 
 void StartGame(interface_mode uMsg)
 {
@@ -194,6 +261,12 @@ void StartGame(interface_mode uMsg)
 	sgnTimeoutCurs = CURSOR_NONE;
 	sgbMouseDown = CLICK_NONE;
 	LastPlayerAction = PlayerActionType::None;
+	hasEnteredActiveGameplay = false;
+	autoSaveCooldownUntil = 0;
+	autoSaveCombatCooldownUntil = 0;
+	pendingAutoSaveReason = AutoSaveReason::None;
+	autoSaveNextTimerDueAt = SDL_GetTicks() + GetAutoSaveIntervalMilliseconds();
+	wasAutoSaveEnabled = *GetOptions().Gameplay.autoSaveEnabled;
 }
 
 void FreeGame()
@@ -1553,6 +1626,32 @@ void GameLogic()
 	RedrawViewport();
 	pfile_update(false);
 
+	if (!hasEnteredActiveGameplay && LastPlayerAction != PlayerActionType::None)
+		hasEnteredActiveGameplay = true;
+
+	const bool autoSaveEnabled = *GetOptions().Gameplay.autoSaveEnabled;
+	if (autoSaveEnabled != wasAutoSaveEnabled) {
+		if (!autoSaveEnabled)
+			pendingAutoSaveReason = AutoSaveReason::None;
+
+		autoSaveNextTimerDueAt = SDL_GetTicks() + GetAutoSaveIntervalMilliseconds();
+		wasAutoSaveEnabled = autoSaveEnabled;
+	}
+
+	if (autoSaveEnabled) {
+		const TickCount now = SDL_GetTicks();
+		if (HaveTicksPassed(now, autoSaveNextTimerDueAt)) {
+			QueueAutoSave(AutoSaveReason::Timer);
+		}
+	}
+
+	if (HasPendingAutoSave() && IsAutoSaveSafe()) {
+		if (AttemptAutoSave(pendingAutoSaveReason)) {
+			pendingAutoSaveReason = AutoSaveReason::None;
+			autoSaveNextTimerDueAt = SDL_GetTicks() + GetAutoSaveIntervalMilliseconds();
+		}
+	}
+
 	plrctrls_after_game_logic();
 }
 
@@ -1802,6 +1901,127 @@ const auto OptionChangeHandlerLanguage = (GetOptions().Language.code.SetValueCha
 
 } // namespace
 
+bool HasActiveMonstersForAutoSave();
+
+bool IsAutoSaveSafe()
+{
+	if (gbIsMultiplayer || !gbRunGame)
+		return false;
+
+	if (!hasEnteredActiveGameplay)
+		return false;
+
+	if (!HaveTicksPassed(autoSaveCooldownUntil))
+		return false;
+
+	if (!HaveTicksPassed(autoSaveCombatCooldownUntil))
+		return false;
+
+	if (movie_playing || PauseMode != 0 || gmenu_is_active() || IsPlayerInStore())
+		return false;
+
+	if (MyPlayer == nullptr || IsPlayerDead() || MyPlayer->_pLvlChanging || LoadingMapObjects)
+		return false;
+
+	if (qtextflag || DropGoldFlag || IsWithdrawGoldOpen || pcurs != CURSOR_HAND)
+		return false;
+
+	if (leveltype != DTYPE_TOWN && HasActiveMonstersForAutoSave())
+		return false;
+
+	return true;
+}
+
+void MarkCombatActivity()
+{
+	autoSaveCombatCooldownUntil = SDL_GetTicks() + AutoSaveCombatCooldownMilliseconds;
+}
+
+bool HasActiveMonstersForAutoSave()
+{
+	for (const Monster &monster : Monsters) {
+		if (monster.hitPoints <= 0 || monster.mode == MonsterMode::Death || monster.mode == MonsterMode::Petrified)
+			continue;
+
+		if (monster.activeForTicks == 0)
+			continue;
+
+		return true;
+	}
+
+	return false;
+}
+
+int GetSecondsUntilNextAutoSave()
+{
+	if (!*GetOptions().Gameplay.autoSaveEnabled)
+		return -1;
+
+	if (HasPendingAutoSave())
+		return 0;
+
+	const TickCount now = SDL_GetTicks();
+	if (HaveTicksPassed(now, autoSaveNextTimerDueAt))
+		return 0;
+
+	const TickCount remainingMilliseconds = autoSaveNextTimerDueAt - now;
+	return static_cast<int>((remainingMilliseconds + 999) / 1000);
+}
+
+bool HasPendingAutoSave()
+{
+	return pendingAutoSaveReason != AutoSaveReason::None;
+}
+
+void RequestAutoSave(AutoSaveReason reason)
+{
+	if (!*GetOptions().Gameplay.autoSaveEnabled)
+		return;
+
+	if (gbIsMultiplayer)
+		return;
+
+	QueueAutoSave(reason);
+}
+
+void QueueAutoSave(AutoSaveReason reason)
+{
+	if (gbIsMultiplayer)
+		return;
+
+	if (!*GetOptions().Gameplay.autoSaveEnabled)
+		return;
+
+	if (GetAutoSavePriority(reason) > GetAutoSavePriority(pendingAutoSaveReason)) {
+		pendingAutoSaveReason = reason;
+		LogVerbose("Autosave queued: {}", GetAutoSaveReasonName(reason));
+	}
+}
+
+bool AttemptAutoSave(AutoSaveReason reason)
+{
+	if (!IsAutoSaveSafe())
+		return false;
+
+	const EventHandler saveProc = SetEventHandler(DisableInputEventHandler);
+	const TickCount currentTime = SDL_GetTicks();
+	const SaveResult saveResult = SaveGame(SaveKind::Auto);
+	const TickCount afterSaveTime = SDL_GetTicks();
+	const bool saveSucceeded = saveResult == SaveResult::Success;
+
+	autoSaveCooldownUntil = afterSaveTime + AutoSaveCooldownMilliseconds;
+	if (saveSucceeded) {
+		autoSaveNextTimerDueAt = afterSaveTime + GetAutoSaveIntervalMilliseconds();
+		if (reason != AutoSaveReason::Timer) {
+			const int timeElapsed = static_cast<int>(afterSaveTime - currentTime);
+			const int displayTime = std::max(500, 1000 - timeElapsed);
+			InitDiabloMsg(EMSG_GAME_SAVED, displayTime);
+		}
+	}
+	SetEventHandler(saveProc);
+	return saveSucceeded;
+}
+
 void InitKeymapActions()
 {
 	Options &options = GetOptions();
@@ -3434,6 +3654,8 @@ tl::expected<void, std::string> LoadGameLevel(bool firstflag, lvl_entry lvldir)
 	CompleteProgress();
 
 	LoadGameLevelCalculateCursor();
+	if (leveltype == DTYPE_TOWN && lvldir != ENTRY_LOAD && !firstflag)
+		::devilution::RequestAutoSave(AutoSaveReason::TownEntry);
 	return {};
 }
 
diff --git a/Source/diablo.h b/Source/diablo.h
index ad28ebb82..86c378cc9 100644
--- a/Source/diablo.h
+++ b/Source/diablo.h
@@ -68,6 +68,14 @@ enum class PlayerActionType : uint8_t {
 	OperateObject,
 };
 
+enum class AutoSaveReason : uint8_t {
+	None,
+	Timer,
+	TownEntry,
+	BossKill,
+	UniquePickup,
+};
+
 extern uint32_t DungeonSeeds[NUMLEVELS];
 extern DVL_API_FOR_TEST std::optional<uint32_t> LevelSeeds[NUMLEVELS];
 extern Point MousePosition;
@@ -101,6 +109,13 @@ bool PressEscKey();
 void DisableInputEventHandler(const SDL_Event &event, uint16_t modState);
 tl::expected<void, std::string> LoadGameLevel(bool firstflag, lvl_entry lvldir);
 bool IsDiabloAlive(bool playSFX);
+void MarkCombatActivity();
+bool IsAutoSaveSafe();
+int GetSecondsUntilNextAutoSave();
+bool HasPendingAutoSave();
+void RequestAutoSave(AutoSaveReason reason);
+void QueueAutoSave(AutoSaveReason reason);
+bool AttemptAutoSave(AutoSaveReason reason);
 void PrintScreen(SDL_Keycode vkey);
 
 /**
diff --git a/Source/gamemenu.cpp b/Source/gamemenu.cpp
index f1f997c75..47ba4b5e2 100644
--- a/Source/gamemenu.cpp
+++ b/Source/gamemenu.cpp
@@ -5,11 +5,15 @@
  */
 #include "gamemenu.h"
 
+#include <fmt/format.h>
+#include <string>
+
 #ifdef USE_SDL3
 #include <SDL3/SDL_timer.h>
 #endif
 
 #include "cursor.h"
+#include "diablo.h"
 #include "diablo_msg.hpp"
 #include "engine/backbuffer_state.hpp"
 #include "engine/demomode.h"
@@ -36,6 +40,9 @@ bool isGameMenuOpen = false;
 
 namespace {
 
+constexpr const char *SaveFailedPreservedMessage = N_("Save failed. The previous save is still available.");
+constexpr const char *SaveFailedNoValidMessage = N_("Save failed. No valid save is available.");
+
 // Forward-declare menu handlers, used by the global menu structs below.
 void GamemenuPrevious(bool bActivate);
 void GamemenuNewGame(bool bActivate);
@@ -89,6 +96,8 @@ const char *const SoundToggleNames[] = {
 	N_("Sound Disabled"),
 };
 
+std::string saveGameMenuLabel;
+
 void GamemenuUpdateSingle()
 {
 	sgSingleMenu[2].setEnabled(gbValidSaveFile);
@@ -98,6 +107,27 @@ void GamemenuUpdateSingle()
 	sgSingleMenu[0].setEnabled(enable);
 }
 
+std::string_view GetSaveGameMenuLabel()
+{
+#ifndef _DEBUG
+	return _("Save Game");
+#else
+	if (HasPendingAutoSave()) {
+		saveGameMenuLabel = fmt::format(fmt::runtime(_("Save Game ({:s})")), _("ready"));
+		return saveGameMenuLabel;
+	}
+
+	const int seconds = GetSecondsUntilNextAutoSave();
+	if (seconds < 0) {
+		saveGameMenuLabel = _("Save Game");
+		return saveGameMenuLabel;
+	}
+
+	saveGameMenuLabel = fmt::format(fmt::runtime(_("Save Game ({:d})")), seconds);
+	return saveGameMenuLabel;
+#endif
+}
+
 void GamemenuPrevious(bool /*bActivate*/)
 {
 	gamemenu_on();
@@ -350,12 +380,26 @@ void gamemenu_save_game(bool /*bActivate*/)
 	RedrawEverything();
 	DrawAndBlit();
 	const uint32_t currentTime = SDL_GetTicks();
-	SaveGame();
+	const SaveResult saveResult = SaveGame(SaveKind::Manual);
 	ClrDiabloMsg();
-	InitDiabloMsg(EMSG_GAME_SAVED, currentTime + 1000 - SDL_GetTicks());
+	switch (saveResult) {
+	case SaveResult::Success: {
+		const uint32_t afterSaveTime = SDL_GetTicks();
+		const int timeElapsed = static_cast<int>(afterSaveTime - currentTime);
+		const int displayTime = std::max(500, 1000 - timeElapsed);
+		InitDiabloMsg(EMSG_GAME_SAVED, displayTime);
+		break;
+	}
+	case SaveResult::FailedButPreviousSavePreserved:
+		InitDiabloMsg(_(SaveFailedPreservedMessage));
+		break;
+	case SaveResult::FailedNoValidSave:
+		InitDiabloMsg(_(SaveFailedNoValidMessage));
+		break;
+	}
 	RedrawEverything();
 	NewCursor(CURSOR_HAND);
-	if (CornerStone.activated) {
+	if (saveResult == SaveResult::Success && CornerStone.activated) {
 		CornerstoneSave();
 		if (!demo::IsRunning()) SaveOptions();
 	}
@@ -363,6 +407,14 @@ void gamemenu_save_game(bool /*bActivate*/)
 	SetEventHandler(saveProc);
 }
 
+std::string_view GetGamemenuText(const TMenuItem &menuItem)
+{
+	if (menuItem.fnMenu == &gamemenu_save_game)
+		return GetSaveGameMenuLabel();
+
+	return _(menuItem.pszStr);
+}
+
 void gamemenu_on()
 {
 	isGameMenuOpen = true;
diff --git a/Source/gamemenu.h b/Source/gamemenu.h
index 1b6abd731..1024e5db6 100644
--- a/Source/gamemenu.h
+++ b/Source/gamemenu.h
@@ -5,8 +5,12 @@
  */
 #pragma once
 
+#include <string_view>
+
 namespace devilution {
 
+struct TMenuItem;
+
 void gamemenu_on();
 void gamemenu_off();
 void gamemenu_handle_previous();
@@ -14,6 +18,7 @@ void gamemenu_exit_game(bool bActivate);
 void gamemenu_quit_game(bool bActivate);
 void gamemenu_load_game(bool bActivate);
 void gamemenu_save_game(bool bActivate);
+std::string_view GetGamemenuText(const TMenuItem &menuItem);
 
 extern bool isGameMenuOpen;
 
diff --git a/Source/gmenu.cpp b/Source/gmenu.cpp
index 6e1c5230d..df1c026a5 100644
--- a/Source/gmenu.cpp
+++ b/Source/gmenu.cpp
@@ -29,6 +29,7 @@
 #include "engine/render/clx_render.hpp"
 #include "engine/render/primitive_render.hpp"
 #include "engine/render/text_render.hpp"
+#include "gamemenu.h"
 #include "headless_mode.hpp"
 #include "options.h"
 #include "stores.h"
@@ -123,11 +124,12 @@ int GmenuGetLineWidth(TMenuItem *pItem)
 	if (pItem->isSlider())
 		return SliderItemWidth;
 
-	return GetLineWidth(_(pItem->pszStr), GameFont46, 2);
+	return GetLineWidth(GetGamemenuText(*pItem), GameFont46, 2);
 }
 
 void GmenuDrawMenuItem(const Surface &out, TMenuItem *pItem, int y)
 {
+	const std::string_view menuText = GetGamemenuText(*pItem);
 	const int w = GmenuGetLineWidth(pItem);
 	if (pItem->isSlider()) {
 		const int uiPositionX = GetUIRectangle().position.x;
@@ -142,7 +144,7 @@ void GmenuDrawMenuItem(const Surface &out, TMenuItem *pItem, int y)
 
 	const int x = (gnScreenWidth - w) / 2;
 	const UiFlags style = pItem->enabled() ? UiFlags::ColorGold : UiFlags::ColorBlack;
-	DrawString(out, _(pItem->pszStr), Point { x, y },
+	DrawString(out, menuText, Point { x, y },
 	    { .flags = style | UiFlags::FontSize46, .spacing = 2 });
 	if (pItem == sgpCurrItem) {
 		const ClxSprite sprite = (*PentSpin_cel)[PentSpn2Spin()];
diff --git a/Source/inv.cpp b/Source/inv.cpp
index fc97994c9..202ecd6e7 100644
--- a/Source/inv.cpp
+++ b/Source/inv.cpp
@@ -22,6 +22,7 @@
 #include "controls/control_mode.hpp"
 #include "controls/plrctrls.h"
 #include "cursor.h"
+#include "diablo.h"
 #include "engine/backbuffer_state.hpp"
 #include "engine/clx_sprite.hpp"
 #include "engine/load_cel.hpp"
@@ -1691,8 +1692,12 @@ void InvGetItem(Player &player, int ii)
 		NewCursor(player.HoldItem);
 	}
 
+	const bool pickedUniqueItem = &player == MyPlayer && item._iMagical == ITEM_QUALITY_UNIQUE;
+
 	// This potentially moves items in memory so must be done after we've made a copy
 	CleanupItems(ii);
+	if (pickedUniqueItem)
+		RequestAutoSave(AutoSaveReason::UniquePickup);
 	pcursitem = -1;
 }
 
@@ -1771,7 +1776,10 @@ void AutoGetItem(Player &player, Item *itemPointer, int ii)
 			PlaySFX(SfxID::GrabItem);
 		}
 
+		const bool pickedUniqueItem = &player == MyPlayer && item._iMagical == ITEM_QUALITY_UNIQUE;
 		CleanupItems(ii);
+		if (pickedUniqueItem)
+			RequestAutoSave(AutoSaveReason::UniquePickup);
 		return;
 	}
 
diff --git a/Source/loadsave.cpp b/Source/loadsave.cpp
index 010658713..5043df630 100644
--- a/Source/loadsave.cpp
+++ b/Source/loadsave.cpp
@@ -57,6 +57,41 @@ constexpr size_t PlayerWalkPathSizeForSaveGame = 25;
 uint8_t giNumberQuests;
 uint8_t giNumberOfSmithPremiumItems;
 
+bool ActiveSaveContainsGame()
+{
+	if (gbIsMultiplayer)
+		return false;
+
+	auto archive = OpenSaveArchive(gSaveNumber);
+	if (!archive)
+		return false;
+
+	auto gameData = ReadArchive(*archive, "game");
+	if (gameData == nullptr)
+		return false;
+
+	return IsHeaderValid(LoadLE32(gameData.get()));
+}
+
+bool ActiveSaveContainsStash()
+{
+	auto archive = OpenStashArchive();
+	if (!archive)
+		return true;
+
+	const char *stashFileName = gbIsMultiplayer ? "mpstashitems" : "spstashitems";
+	return ReadArchive(*archive, stashFileName) != nullptr;
+}
+
+SaveResult GetSaveFailureResult()
+{
+	const bool hasValidGame = ActiveSaveContainsGame();
+	const bool hasValidStash = ActiveSaveContainsStash();
+
+	gbValidSaveFile = hasValidGame;
+	return (hasValidGame && hasValidStash) ? SaveResult::FailedButPreviousSavePreserved : SaveResult::FailedNoValidSave;
+}
+
 template <class T>
 T SwapLE(T in)
 {
@@ -2680,7 +2715,7 @@ tl::expected<void, std::string> LoadGame(bool firstflag)
 	gbProcessPlayers = IsDiabloAlive(!firstflag);
 
 	if (gbIsHellfireSaveGame != gbIsHellfire) {
-		SaveGame();
+		SaveGame(SaveKind::System);
 	}
 
 	gbIsHellfireSaveGame = gbIsHellfire;
@@ -2926,11 +2961,41 @@ void SaveGameData(SaveWriter &saveWriter)
 	SaveLevelSeeds(saveWriter);
 }
 
-void SaveGame()
+SaveResult SaveGame(SaveKind kind)
 {
-	gbValidSaveFile = true;
+#if defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM)
 	pfile_write_hero(/*writeGameData=*/true);
 	sfile_write_stash();
+	gbValidSaveFile = true;
+	return SaveResult::Success;
+#else
+	switch (kind) {
+	case SaveKind::Manual:
+		if (!pfile_write_manual_game_with_backup())
+			return GetSaveFailureResult();
+		break;
+	case SaveKind::Auto:
+	case SaveKind::System:
+		if (!pfile_write_auto_game())
+			return GetSaveFailureResult();
+		break;
+	}
+
+	gbValidSaveFile = true;
+	switch (kind) {
+	case SaveKind::Manual:
+		if (!pfile_write_manual_stash_with_backup())
+			return GetSaveFailureResult();
+		break;
+	case SaveKind::Auto:
+	case SaveKind::System:
+		if (!pfile_write_auto_stash())
+			return GetSaveFailureResult();
+		break;
+	}
+
+	return SaveResult::Success;
+#endif
 }
 
 void SaveLevel(SaveWriter &saveWriter)
diff --git a/Source/loadsave.h b/Source/loadsave.h
index 0d139e143..071dffb17 100644
--- a/Source/loadsave.h
+++ b/Source/loadsave.h
@@ -18,6 +18,18 @@ namespace devilution {
 extern DVL_API_FOR_TEST bool gbIsHellfireSaveGame;
 extern DVL_API_FOR_TEST uint8_t giNumberOfLevels;
 
+enum class SaveKind : uint8_t {
+	Manual,
+	Auto,
+	System,
+};
+
+enum class SaveResult : uint8_t {
+	Success,
+	FailedButPreviousSavePreserved,
+	FailedNoValidSave,
+};
+
 void RemoveInvalidItem(Item &pItem);
 _item_indexes RemapItemIdxFromDiablo(_item_indexes i);
 _item_indexes RemapItemIdxToDiablo(_item_indexes i);
@@ -40,7 +52,7 @@ tl::expected<void, std::string> LoadGame(bool firstflag);
 void SaveHotkeys(SaveWriter &saveWriter, const Player &player);
 void SaveHeroItems(SaveWriter &saveWriter, Player &player);
 void SaveGameData(SaveWriter &saveWriter);
-void SaveGame();
+SaveResult SaveGame(SaveKind kind);
 void SaveLevel(SaveWriter &saveWriter);
 tl::expected<void, std::string> LoadLevel();
 tl::expected<void, std::string> ConvertLevels(SaveWriter &saveWriter);
diff --git a/Source/monster.cpp b/Source/monster.cpp
index e8905a23d..5a935cda0 100644
--- a/Source/monster.cpp
+++ b/Source/monster.cpp
@@ -4025,6 +4025,8 @@ void MonsterDeath(Monster &monster, Direction md, bool sendmsg)
 	M_ClearSquares(monster);
 	monster.occupyTile(monster.position.tile, false);
 	CheckQuestKill(monster, sendmsg);
+	if (!gbIsMultiplayer && IsAnyOf(monster.type().type, MT_CLEAVER, MT_SKING, MT_DIABLO, MT_DEFILER, MT_NAKRUL))
+		RequestAutoSave(AutoSaveReason::BossKill);
 	M_FallenFear(monster.position.tile);
 	if (IsAnyOf(monster.type().type, MT_NACID, MT_RACID, MT_BACID, MT_XACID, MT_SPIDLORD))
 		AddMissile(monster.position.tile, { 0, 0 }, Direction::South, MissileID::AcidPuddle, TARGET_PLAYERS, monster, monster.intelligence + 1, 0);
diff --git a/Source/options.cpp b/Source/options.cpp
index 52e2730ed..5a8a91439 100644
--- a/Source/options.cpp
+++ b/Source/options.cpp
@@ -865,6 +865,12 @@ GameplayOptions::GameplayOptions()
     , autoRefillBelt("Auto Refill Belt", OptionEntryFlags::None, N_("Auto Refill Belt"), N_("Refill belt from inventory when belt item is consumed."), false)
     , disableCripplingShrines("Disable Crippling Shrines", OptionEntryFlags::None, N_("Disable Crippling Shrines"), N_("When enabled Cauldrons, Fascinating Shrines, Goat Shrines, Ornate Shrines, Sacred Shrines and Murphy's Shrines are not able to be clicked on and labeled as disabled."), false)
     , quickCast("Quick Cast", OptionEntryFlags::None, N_("Quick Cast"), N_("Spell hotkeys instantly cast the spell, rather than switching the readied spell."), false)
+    , autoSaveEnabled("Auto Save", OptionEntryFlags::CantChangeInMultiPlayer, N_("Auto Save"), N_("Autosave works only in single player and only at safe moments."), false)
+#ifdef _DEBUG
+    , autoSaveIntervalSeconds("Auto Save Interval", OptionEntryFlags::CantChangeInMultiPlayer, N_("Autosave interval (seconds)"), N_("Time between periodic autosave attempts."), 120, { 30, 60, 90, 120, 180, 300, 600 })
+#else
+    , autoSaveIntervalSeconds("Auto Save Interval", OptionEntryFlags::CantChangeInMultiPlayer | OptionEntryFlags::Invisible, "", "", 120, { 30, 60, 90, 120, 180, 300, 600 })
+#endif
     , numHealPotionPickup("Heal Potion Pickup", OptionEntryFlags::None, N_("Heal Potion Pickup"), N_("Number of Healing potions to pick up automatically."), 0, { 0, 1, 2, 4, 8, 16 })
     , numFullHealPotionPickup("Full Heal Potion Pickup", OptionEntryFlags::None, N_("Full Heal Potion Pickup"), N_("Number of Full Healing potions to pick up automatically."), 0, { 0, 1, 2, 4, 8, 16 })
     , numManaPotionPickup("Mana Potion Pickup", OptionEntryFlags::None, N_("Mana Potion Pickup"), N_("Number of Mana potions to pick up automatically."), 0, { 0, 1, 2, 4, 8, 16 })
@@ -886,6 +892,10 @@ std::vector<OptionEntryBase *> GameplayOptions::GetEntries()
 		&cowQuest,
 		&runInTown,
 		&quickCast,
+		&autoSaveEnabled,
+#ifdef _DEBUG
+		&autoSaveIntervalSeconds,
+#endif
 		&testBard,
 		&testBarbarian,
 		&experienceBar,
diff --git a/Source/options.h b/Source/options.h
index 58954f55f..41e00dbf0 100644
--- a/Source/options.h
+++ b/Source/options.h
@@ -623,6 +623,10 @@ struct GameplayOptions : OptionCategoryBase {
 	OptionEntryBoolean disableCripplingShrines;
 	/** @brief Spell hotkeys instantly cast the spell. */
 	OptionEntryBoolean quickCast;
+	/** @brief Enable periodic and event-driven automatic save in single player. */
+	OptionEntryBoolean autoSaveEnabled;
+	/** @brief Time in seconds between automatic save attempts. */
+	OptionEntryInt<int> autoSaveIntervalSeconds;
 	/** @brief Number of Healing potions to pick up automatically */
 	OptionEntryInt<int> numHealPotionPickup;
 	/** @brief Number of Full Healing potions to pick up automatically */
diff --git a/Source/pfile.cpp b/Source/pfile.cpp
index ec96c6608..a77dc0e07 100644
--- a/Source/pfile.cpp
+++ b/Source/pfile.cpp
@@ -76,9 +76,9 @@ std::string GetSavePath(uint32_t saveNum, std::string_view savePrefix = {})
 	);
 }
 
-std::string GetStashSavePath()
+std::string GetStashSavePath(std::string_view savePrefix = {})
 {
-	return StrCat(paths::PrefPath(),
+	return StrCat(paths::PrefPath(), savePrefix,
 	    gbIsSpawn ? "stash_spawn" : "stash",
 #ifdef UNPACKED_SAVES
 	    gbIsHellfire ? "_hsv" DIRECTORY_SEPARATOR_STR : "_sv" DIRECTORY_SEPARATOR_STR
@@ -170,22 +170,57 @@ SaveWriter GetStashWriter()
 	return SaveWriter(GetStashSavePath());
 }
 
-#ifndef DISABLE_DEMOMODE
-void CopySaveFile(uint32_t saveNum, std::string targetPath)
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
+bool SaveLocationExists(const std::string &location)
+{
+	return FileExists(location.c_str()) || DirectoryExists(location.c_str());
+}
+
+void CopySaveLocation(const std::string &sourceLocation, const std::string &targetLocation)
 {
-	const std::string savePath = GetSavePath(saveNum);
 #if defined(UNPACKED_SAVES)
-#ifdef DVL_NO_FILESYSTEM
-#error "UNPACKED_SAVES requires either DISABLE_DEMOMODE or C++17 <filesystem>"
+	if (!targetLocation.empty()) {
+		CreateDir(targetLocation.c_str());
+	}
+	for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(sourceLocation)) {
+		const std::filesystem::path targetFilePath = std::filesystem::path(targetLocation) / entry.path().filename();
+		CopyFileOverwrite(entry.path().string().c_str(), targetFilePath.string().c_str());
+	}
+#else
+	CopyFileOverwrite(sourceLocation.c_str(), targetLocation.c_str());
 #endif
-	if (!targetPath.empty()) {
-		CreateDir(targetPath.c_str());
+}
+
+void RestoreSaveLocation(const std::string &targetLocation, const std::string &backupLocation)
+{
+#if defined(UNPACKED_SAVES)
+	if (DirectoryExists(targetLocation.c_str())) {
+		for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(targetLocation))
+			RemoveFile(entry.path().string().c_str());
 	}
-	for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(savePath)) {
-		CopyFileOverwrite(entry.path().string().c_str(), (targetPath + entry.path().filename().string()).c_str());
+	CreateDir(targetLocation.c_str());
+	for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(backupLocation)) {
+		const std::filesystem::path restoredFilePath = std::filesystem::path(targetLocation) / entry.path().filename();
+		CopyFileOverwrite(entry.path().string().c_str(), restoredFilePath.string().c_str());
 	}
 #else
-	CopyFileOverwrite(savePath.c_str(), targetPath.c_str());
+	CopyFileOverwrite(backupLocation.c_str(), targetLocation.c_str());
+#endif
+}
+
+void DeleteSaveLocation(const std::string &location)
+{
+#if defined(UNPACKED_SAVES)
+	if (!DirectoryExists(location.c_str()))
+		return;
+
+	for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(location))
+		RemoveFile(entry.path().string().c_str());
+
+	std::filesystem::remove(location);
+#else
+	if (FileExists(location.c_str()))
+		RemoveFile(location.c_str());
 #endif
 }
 #endif
@@ -629,12 +664,118 @@ void pfile_write_hero(bool writeGameData)
 	pfile_write_hero(saveWriter, writeGameData);
 }
 
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
+bool SaveWrittenGameIsValid()
+{
+	auto archive = OpenSaveArchive(gSaveNumber);
+	return archive && ArchiveContainsGame(*archive);
+}
+
+bool WriteGameAndRestoreOnFailure(const std::string &restoreLocation)
+{
+	const bool hasRestoreLocation = SaveLocationExists(restoreLocation);
+
+	pfile_write_hero(/*writeGameData=*/true);
+
+	if (SaveWrittenGameIsValid())
+		return true;
+
+	if (!hasRestoreLocation)
+		return false;
+
+	RestoreSaveLocation(GetSavePath(gSaveNumber), restoreLocation);
+	return false;
+}
+
+bool pfile_write_manual_game_with_backup()
+{
+	const std::string backupPrefix = "backup_";
+	const std::string backupLocation = GetSavePath(gSaveNumber, backupPrefix);
+	const std::string saveLocation = GetSavePath(gSaveNumber);
+
+	if (SaveLocationExists(saveLocation))
+		CopySaveLocation(saveLocation, backupLocation);
+
+	return WriteGameAndRestoreOnFailure(backupLocation);
+}
+
+bool pfile_write_auto_game()
+{
+	const std::string restorePrefix = "autosave_restore_";
+	const std::string restoreLocation = GetSavePath(gSaveNumber, restorePrefix);
+	const std::string saveLocation = GetSavePath(gSaveNumber);
+
+	if (SaveLocationExists(saveLocation))
+		CopySaveLocation(saveLocation, restoreLocation);
+
+	const bool saveIsValid = WriteGameAndRestoreOnFailure(restoreLocation);
+	DeleteSaveLocation(restoreLocation);
+	return saveIsValid;
+}
+
+bool WriteStashAndRestoreOnFailure(std::string_view restorePrefix, bool deleteRestoreLocationOnSuccess)
+{
+	if (!Stash.dirty)
+		return true;
+
+	const std::string restoreLocation = GetStashSavePath(restorePrefix);
+	const std::string stashLocation = GetStashSavePath();
+
+	SaveWriter stashWriter = GetStashWriter();
+	SaveStash(stashWriter);
+
+	auto archive = OpenStashArchive();
+	const char *stashFileName = gbIsMultiplayer ? "mpstashitems" : "spstashitems";
+	const bool stashIsValid = archive && ReadArchive(*archive, stashFileName) != nullptr;
+	if (stashIsValid) {
+		Stash.dirty = false;
+		if (deleteRestoreLocationOnSuccess)
+			DeleteSaveLocation(restoreLocation);
+		return true;
+	}
+
+	if (!SaveLocationExists(restoreLocation))
+		return false;
+
+	RestoreSaveLocation(stashLocation, restoreLocation);
+	return false;
+}
+
+bool pfile_write_manual_stash_with_backup()
+{
+	const std::string backupPrefix = "backup_";
+	const std::string backupLocation = GetStashSavePath(backupPrefix);
+	const std::string stashLocation = GetStashSavePath();
+
+	if (SaveLocationExists(stashLocation))
+		CopySaveLocation(stashLocation, backupLocation);
+
+	return WriteStashAndRestoreOnFailure(backupPrefix, false);
+}
+
+bool pfile_write_auto_stash()
+{
+	const std::string restorePrefix = "autosave_restore_";
+	const std::string restoreLocation = GetStashSavePath(restorePrefix);
+	const std::string stashLocation = GetStashSavePath();
+
+	if (SaveLocationExists(stashLocation))
+		CopySaveLocation(stashLocation, restoreLocation);
+
+	const bool stashIsValid = WriteStashAndRestoreOnFailure(restorePrefix, true);
+	if (!stashIsValid && SaveLocationExists(restoreLocation))
+		DeleteSaveLocation(restoreLocation);
+	return stashIsValid;
+}
+#endif
+
 #ifndef DISABLE_DEMOMODE
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
 void pfile_write_hero_demo(int demo)
 {
-	const std::string savePath = GetSavePath(gSaveNumber, StrCat("demo_", demo, "_reference_"));
-	CopySaveFile(gSaveNumber, savePath);
-	auto saveWriter = SaveWriter(savePath.c_str());
+	const std::string saveLocation = GetSavePath(gSaveNumber, StrCat("demo_", demo, "_reference_"));
+	CopySaveLocation(GetSavePath(gSaveNumber), saveLocation);
+	auto saveWriter = SaveWriter(saveLocation.c_str());
 	pfile_write_hero(saveWriter, true);
 }
 
@@ -647,13 +788,27 @@ HeroCompareResult pfile_compare_hero_demo(int demo, bool logDetails)
 
 	const std::string actualSavePath = GetSavePath(gSaveNumber, StrCat("demo_", demo, "_actual_"));
 	{
-		CopySaveFile(gSaveNumber, actualSavePath);
+		CopySaveLocation(GetSavePath(gSaveNumber), actualSavePath);
 		SaveWriter saveWriter(actualSavePath.c_str());
 		pfile_write_hero(saveWriter, true);
 	}
 
 	return CompareSaves(actualSavePath, referenceSavePath, logDetails);
 }
+#else
+// Demo save comparison is unavailable on UNPACKED_SAVES targets without filesystem support.
+void pfile_write_hero_demo(int demo)
+{
+	(void)demo;
+}
+
+HeroCompareResult pfile_compare_hero_demo(int demo, bool logDetails)
+{
+	(void)demo;
+	(void)logDetails;
+	return { HeroCompareResult::ReferenceNotFound, {} };
+}
+#endif
 #endif
 
 void sfile_write_stash()
diff --git a/Source/pfile.h b/Source/pfile.h
index df10fca08..d41c00d44 100644
--- a/Source/pfile.h
+++ b/Source/pfile.h
@@ -101,6 +101,10 @@ std::optional<SaveReader> OpenStashArchive();
 const char *pfile_get_password();
 std::unique_ptr<std::byte[]> ReadArchive(SaveReader &archive, const char *pszName, size_t *pdwLen = nullptr);
 void pfile_write_hero(bool writeGameData = false);
+bool pfile_write_manual_game_with_backup();
+bool pfile_write_auto_game();
+bool pfile_write_manual_stash_with_backup();
+bool pfile_write_auto_stash();
 
 #ifndef DISABLE_DEMOMODE
 /**
diff --git a/Source/player.cpp b/Source/player.cpp
index 1b6f14096..ba21a1fc9 100644
--- a/Source/player.cpp
+++ b/Source/player.cpp
@@ -24,6 +24,7 @@
 #ifdef _DEBUG
 #include "debug.h"
 #endif
+#include "diablo.h"
 #include "engine/backbuffer_state.hpp"
 #include "engine/load_cl2.hpp"
 #include "engine/load_file.hpp"
@@ -179,6 +180,9 @@ void StartAttack(Player &player, Direction d, bool includesFirstFrame)
 		return;
 	}
 
+	if (&player == MyPlayer && IsAnyOf(LastPlayerAction, PlayerActionType::AttackMonsterTarget, PlayerActionType::AttackPlayerTarget))
+		MarkCombatActivity();
+
 	int8_t skippedAnimationFrames = 0;
 	const auto flags = player._pIFlags;
 
@@ -211,6 +215,9 @@ void StartRangeAttack(Player &player, Direction d, WorldTileCoord cx, WorldTileC
 		return;
 	}
 
+	if (&player == MyPlayer)
+		MarkCombatActivity();
+
 	int8_t skippedAnimationFrames = 0;
 	const auto flags = player._pIFlags;
 
@@ -246,6 +253,17 @@ player_graphic GetPlayerGraphicForSpell(SpellID spellId)
 	}
 }
 
+bool IsSpellOffensiveForAutoSave(SpellID spellId)
+{
+	const SpellData &spellData = GetSpellData(spellId);
+	for (MissileID missileId : spellData.sMissiles) {
+		if (missileId != MissileID::Null)
+			return true;
+	}
+
+	return false;
+}
+
 void StartSpell(Player &player, Direction d, WorldTileCoord cx, WorldTileCoord cy)
 {
 	if (player._pInvincible && player.hasNoLife() && &player == MyPlayer) {
@@ -272,6 +290,9 @@ void StartSpell(Player &player, Direction d, WorldTileCoord cx, WorldTileCoord c
 	if (!isValid)
 		return;
 
+	if (&player == MyPlayer && IsSpellOffensiveForAutoSave(player.queuedSpell.spellId))
+		MarkCombatActivity();
+
 	auto animationFlags = AnimationDistributionFlags::ProcessAnimationPending;
 	if (player._pmode == PM_SPELL)
 		animationFlags = static_cast<AnimationDistributionFlags>(animationFlags | AnimationDistributionFlags::RepeatedAction);
@@ -761,6 +782,8 @@ bool PlrHitPlr(Player &attacker, Player &target)
 	if (&attacker == MyPlayer) {
 		NetSendCmdDamage(true, target, skdam, DamageType::Physical);
 	}
+	if (&attacker == MyPlayer && skdam > 0)
+		MarkCombatActivity();
 	StartPlrHit(target, skdam, false);
 
 	return true;
@@ -2823,6 +2846,8 @@ void StripTopGold(Player &player)
 void ApplyPlrDamage(DamageType damageType, Player &player, int dam, int minHP /*= 0*/, int frac /*= 0*/, DeathReason deathReason /*= DeathReason::MonsterOrTrap*/)
 {
 	int totalDamage = (dam << 6) + frac;
+	if (&player == MyPlayer && totalDamage > 0)
+		MarkCombatActivity();
 	if (&player == MyPlayer && !player.hasNoLife()) {
 		lua::OnPlayerTakeDamage(&player, totalDamage, static_cast<int>(damageType));
 	}
diff --git a/Source/utils/sdl2_backports.h b/Source/utils/sdl2_backports.h
index f1c3f584d..cefc8a223 100644
--- a/Source/utils/sdl2_backports.h
+++ b/Source/utils/sdl2_backports.h
@@ -7,6 +7,10 @@
 #define SDL_MAX_UINT32 ((Uint32)0xFFFFFFFFu)
 #endif
 
+#ifndef SDL_TICKS_PASSED
+#define SDL_TICKS_PASSED(A, B) ((Sint32)((B) - (A)) <= 0)
+#endif
+
 #if !SDL_VERSION_ATLEAST(2, 0, 4)
 inline SDL_bool SDL_PointInRect(const SDL_Point *p, const SDL_Rect *r)
 {
diff --git a/Source/utils/sdl2_to_1_2_backports.h b/Source/utils/sdl2_to_1_2_backports.h
index 2a18cca66..5e13df332 100644
--- a/Source/utils/sdl2_to_1_2_backports.h
+++ b/Source/utils/sdl2_to_1_2_backports.h
@@ -26,6 +26,7 @@
 #define SDL_floor floor
 
 #define SDL_MAX_UINT32 ((Uint32)0xFFFFFFFFu)
+#define SDL_TICKS_PASSED(A, B) ((Sint32)((B) - (A)) <= 0)
 
 //== Events handling