diff --git a/client/CPlayerInterface.cpp b/client/CPlayerInterface.cpp
index 1a8aa7cf8..ac99a12ba 100644
--- a/client/CPlayerInterface.cpp
+++ b/client/CPlayerInterface.cpp
@@ -1639,15 +1639,6 @@ void CPlayerInterface::showMarketWindow(const IMarket * market, const CGHeroInst
 		cb->selectionMade(0, queryID);
 	};
 
-	if (market->allowsTrade(EMarketMode::ARTIFACT_EXP) && market->getArtifactsStorage() == nullptr)
-	{
-		// compatibility check, safe to remove for 1.6
-		// 1.4 saves loaded in 1.5 will not be able to visit Altar of Sacrifice due to Altar now requiring different map object class
-		static_assert(ESerializationVersion::RELEASE_143 < ESerializationVersion::CURRENT, "Please remove this compatibility check once it no longer needed");
-		onWindowClosed();
-		return;
-	}
-
 	if(market->allowsTrade(EMarketMode::ARTIFACT_EXP) && visitor->getAlignment() != EAlignment::EVIL)
 		GH.windows().createAndPushWindow<CMarketWindow>(market, visitor, onWindowClosed, EMarketMode::ARTIFACT_EXP);
 	else if(market->allowsTrade(EMarketMode::CREATURE_EXP) && visitor->getAlignment() != EAlignment::GOOD)
diff --git a/lib/CPlayerState.h b/lib/CPlayerState.h
index d834e3f82..a901fd908 100644
--- a/lib/CPlayerState.h
+++ b/lib/CPlayerState.h
@@ -137,13 +137,11 @@ public:
 		h & daysWithoutCastle;
 		h & cheated;
 		h & battleBonuses;
-		if (h.version >= Handler::Version::ARTIFACT_COSTUMES)
-			h & costumesArtifacts;
+		h & costumesArtifacts;
 		h & enteredLosingCheatCode;
 		h & enteredWinningCheatCode;
 		h & static_cast<CBonusSystemNode&>(*this);
-		if (h.version >= Handler::Version::DESTROYED_OBJECTS)
-			h & destroyedObjects;
+		h & destroyedObjects;
 	}
 };
 
diff --git a/lib/StartInfo.h b/lib/StartInfo.h
index 4b5c173ad..6a79ff862 100644
--- a/lib/StartInfo.h
+++ b/lib/StartInfo.h
@@ -52,9 +52,10 @@ struct DLL_LINKAGE SimturnsInfo
 		h & optionalTurns;
 		h & allowHumanWithAI;
 
-		static_assert(Handler::Version::RELEASE_143 < Handler::Version::CURRENT, "Please add ignoreAlliedContacts to serialization for 1.6");
-		// disabled to allow multiplayer compatibility between 1.5.2 and 1.5.1
-		// h & ignoreAlliedContacts
+		if (h.version >= Handler::Version::SAVE_COMPATIBILITY_FIXES)
+			h & ignoreAlliedContacts;
+		else
+			ignoreAlliedContacts = true;
 	}
 };
 
@@ -183,10 +184,7 @@ struct DLL_LINKAGE StartInfo : public Serializeable
 		h & fileURI;
 		h & simturnsInfo;
 		h & turnTimerInfo;
-		if(h.version >= Handler::Version::HAS_EXTRA_OPTIONS)
-			h & extraOptionsInfo;
-		else
-			extraOptionsInfo = ExtraOptionsInfo();
+		h & extraOptionsInfo;
 		h & mapname;
 		h & mapGenOptions;
 		h & campState;
diff --git a/lib/bonuses/Bonus.h b/lib/bonuses/Bonus.h
index 383c4f11f..63b4d6b1d 100644
--- a/lib/bonuses/Bonus.h
+++ b/lib/bonuses/Bonus.h
@@ -95,15 +95,7 @@ struct DLL_LINKAGE Bonus : public std::enable_shared_from_this<Bonus>, public Se
 		h & source;
 		h & val;
 		h & sid;
-		if (h.version < Handler::Version::BONUS_META_STRING)
-		{
-			std::string oldDescription;
-			h & oldDescription;
-			description = MetaString::createFromRawString(oldDescription);
-		}
-		else
-			h & description;
-
+		h & description;
 		h & additionalInfo;
 		h & turnsRemain;
 		h & valType;
@@ -114,11 +106,6 @@ struct DLL_LINKAGE Bonus : public std::enable_shared_from_this<Bonus>, public Se
 		h & updater;
 		h & propagationUpdater;
 		h & targetSourceType;
-		if (h.version < Handler::Version::MANA_LIMIT && type == BonusType::MANA_PER_KNOWLEDGE_PERCENTAGE)
-		{
-			if (valType == BonusValueType::ADDITIVE_VALUE || valType == BonusValueType::BASE_NUMBER)
-				val *= 100;
-		}
 	}
 
 	template <typename Ptr>
diff --git a/lib/campaign/CampaignState.h b/lib/campaign/CampaignState.h
index 17d91e528..01f2b4bf4 100644
--- a/lib/campaign/CampaignState.h
+++ b/lib/campaign/CampaignState.h
@@ -141,8 +141,7 @@ public:
 		h & modName;
 		h & music;
 		h & encoding;
-		if (h.version >= Handler::Version::RELEASE_143)
-			h & textContainer;
+		h & textContainer;
 	}
 };
 
@@ -342,8 +341,7 @@ public:
 		h & currentMap;
 		h & chosenCampaignBonuses;
 		h & campaignSet;
-		if (h.version >= Handler::Version::CAMPAIGN_MAP_TRANSLATIONS)
-			h & mapTranslations;
+		h & mapTranslations;
 		if (h.version >= Handler::Version::HIGHSCORE_PARAMETERS)
 			h & highscoreParameters;
 	}
diff --git a/lib/json/JsonNode.h b/lib/json/JsonNode.h
index 7ed8ae9ae..f4338423a 100644
--- a/lib/json/JsonNode.h
+++ b/lib/json/JsonNode.h
@@ -152,16 +152,7 @@ public:
 	void serialize(Handler & h)
 	{
 		h & modScope;
-
-		if(h.version >= Handler::Version::JSON_FLAGS)
-		{
-			h & overrideFlag;
-		}
-		else
-		{
-			std::vector<std::string> oldFlags;
-			h & oldFlags;
-		}
+		h & overrideFlag;
 		h & data;
 	}
 };
diff --git a/lib/mapObjects/CGMarket.h b/lib/mapObjects/CGMarket.h
index 8a3a83fff..e1bc5b7df 100644
--- a/lib/mapObjects/CGMarket.h
+++ b/lib/mapObjects/CGMarket.h
@@ -31,7 +31,8 @@ public:
 	int availableUnits(EMarketMode mode, int marketItemSerial) const override; //-1 if unlimited
 	std::set<EMarketMode> availableModes() const override;
 
-	template <typename Handler> void serialize(Handler &h)
+	template <typename Handler>
+	void serialize(Handler &h)
 	{
 		h & static_cast<CGObjectInstance&>(*this);
 		if (h.version < Handler::Version::NEW_MARKETS)
@@ -53,6 +54,7 @@ public:
 	template <typename Handler> void serializeArtifactsAltar(Handler &h)
 	{
 		serialize(h);
+		IMarket::serializeArtifactsAltar(h);
 	}
 };
 
diff --git a/lib/mapObjects/IMarket.h b/lib/mapObjects/IMarket.h
index b163990cb..b4822e732 100644
--- a/lib/mapObjects/IMarket.h
+++ b/lib/mapObjects/IMarket.h
@@ -36,6 +36,11 @@ public:
 	CArtifactSet * getArtifactsStorage() const;
 	bool getOffer(int id1, int id2, int &val1, int &val2, EMarketMode mode) const; //val1 - how many units of id1 player has to give to receive val2 units
 
+	template <typename Handler> void serializeArtifactsAltar(Handler &h)
+	{
+		h & *altarArtifactsStorage;
+	}
+
 private:
 	std::unique_ptr<CArtifactSetAltar> altarArtifactsStorage;
 };
diff --git a/lib/mapping/CMap.h b/lib/mapping/CMap.h
index 13cc4ca29..1542bc6e1 100644
--- a/lib/mapping/CMap.h
+++ b/lib/mapping/CMap.h
@@ -196,14 +196,6 @@ public:
 		h & quests;
 		h & allHeroes;
 
-		if (h.version < Handler::Version::DESTROYED_OBJECTS)
-		{
-			// old save compatibility
-			//FIXME: remove this field after save-breaking change
-			h & questIdentifierToId;
-			resolveQuestIdentifiers();
-		}
-
 		//TODO: viccondetails
 		h & terrain;
 		h & guardingCreaturePositions;
diff --git a/lib/mapping/CMapHeader.h b/lib/mapping/CMapHeader.h
index a197ef44d..f58826134 100644
--- a/lib/mapping/CMapHeader.h
+++ b/lib/mapping/CMapHeader.h
@@ -277,12 +277,16 @@ public:
 		h & width;
 		h & height;
 		h & twoLevel;
-		// FIXME: we should serialize enum's according to their underlying type
-		// should be fixed when we are making breaking change to save compatibility
-		static_assert(Handler::Version::MINIMAL < Handler::Version::RELEASE_143);
-		uint8_t difficultyInteger = static_cast<uint8_t>(difficulty);
-		h & difficultyInteger;
-		difficulty = static_cast<EMapDifficulty>(difficultyInteger);
+
+		if (h.version >= Handler::Version::SAVE_COMPATIBILITY_FIXES)
+			h & difficulty;
+		else
+		{
+			uint8_t difficultyInteger = static_cast<uint8_t>(difficulty);
+			h & difficultyInteger;
+			difficulty = static_cast<EMapDifficulty>(difficultyInteger);
+		}
+
 		h & levelLimit;
 		h & areAnyPlayers;
 		h & players;
diff --git a/lib/networkPacks/PacksForLobby.h b/lib/networkPacks/PacksForLobby.h
index 8cb0d55d6..1477bc98e 100644
--- a/lib/networkPacks/PacksForLobby.h
+++ b/lib/networkPacks/PacksForLobby.h
@@ -55,18 +55,7 @@ struct DLL_LINKAGE LobbyClientConnected : public CLobbyPackToPropagate
 
 		h & clientId;
 		h & hostClientId;
-
-		try
-		{
-			if (h.version >= Handler::Version::RELEASE_152)
-				h & version;
-			else
-				version = ESerializationVersion::RELEASE_150;
-		}
-		 catch (const std::runtime_error &)
-		{
-			version = ESerializationVersion::RELEASE_150;
-		}
+		h & version;
 	}
 };
 
diff --git a/lib/rmg/CMapGenOptions.h b/lib/rmg/CMapGenOptions.h
index d82083553..3f151c435 100644
--- a/lib/rmg/CMapGenOptions.h
+++ b/lib/rmg/CMapGenOptions.h
@@ -77,10 +77,7 @@ public:
 			h & startingTown;
 			h & playerType;
 			h & team;
-			if (h.version >= Handler::Version::RELEASE_143)
-				h & startingHero;
-			else
-				startingHero = HeroTypeID::RANDOM;
+			h & startingHero;
 		}
 	};
 
diff --git a/lib/serializer/ESerializationVersion.h b/lib/serializer/ESerializationVersion.h
index 9913b7f4c..7984bf7f6 100644
--- a/lib/serializer/ESerializationVersion.h
+++ b/lib/serializer/ESerializationVersion.h
@@ -31,25 +31,13 @@ enum class ESerializationVersion : int32_t
 {
 	NONE = 0,
 
-	MINIMAL = 831,
-
-	RELEASE_143, // 832 +text container in campaigns, +starting hero in RMG options
-	HAS_EXTRA_OPTIONS, // 833 +extra options struct as part of startinfo
-	DESTROYED_OBJECTS, // 834 +list of objects destroyed by player
-	CAMPAIGN_MAP_TRANSLATIONS, // 835 +campaigns include translations for its maps
-	JSON_FLAGS, // 836 json uses new format for flags
-	MANA_LIMIT,	// 837 change MANA_PER_KNOWLEDGE to percentage
-	BONUS_META_STRING,	// 838 bonuses use MetaString instead of std::string for descriptions
-	TURN_TIMERS_STATE, // 839 current state of turn timers is serialized
-	ARTIFACT_COSTUMES, // 840 swappable artifacts set added
-
-	RELEASE_150 = ARTIFACT_COSTUMES, // for convenience
+	RELEASE_150 = 840,
+	MINIMAL = RELEASE_150,
 
 	VOTING_SIMTURNS, // 841 - allow modification of simturns duration via vote
 	REMOVE_TEXT_CONTAINER_SIZE_T, // 842 Fixed serialization of size_t from text containers
 	BANK_UNIT_PLACEMENT, // 843 Banks have unit placement flag
 
-	RELEASE_152 = BANK_UNIT_PLACEMENT,
 	RELEASE_156 = BANK_UNIT_PLACEMENT,
 
 	COMPACT_STRING_SERIALIZATION, // 844 - optimized serialization of previously encountered strings
@@ -67,6 +55,7 @@ enum class ESerializationVersion : int32_t
 	STATISTICS_SCREEN, // 856 - extent statistic functions
 	NEW_MARKETS, // 857 - reworked market classes
 	PLAYER_STATE_OWNED_OBJECTS, // 858 - player state stores all owned objects in a single list
+	SAVE_COMPATIBILITY_FIXES, // 859 - implementation of previoulsy postponed changes to serialization
 
-	CURRENT = PLAYER_STATE_OWNED_OBJECTS
+	CURRENT = SAVE_COMPATIBILITY_FIXES
 };
diff --git a/server/CGameHandler.h b/server/CGameHandler.h
index fae268fee..8bb57a113 100644
--- a/server/CGameHandler.h
+++ b/server/CGameHandler.h
@@ -243,9 +243,7 @@ public:
 		h & *heroPool;
 		h & *playerMessages;
 		h & *turnOrder;
-
-		if (h.version >= Handler::Version::TURN_TIMERS_STATE)
-			h & *turnTimerHandler;
+		h & *turnTimerHandler;
 
 #if SCRIPTING_ENABLED
 		JsonNode scriptsState;