diff --git a/AI/BattleAI/AttackPossibility.cpp b/AI/BattleAI/AttackPossibility.cpp
index e2fb50dc7..d74ebbd8f 100644
--- a/AI/BattleAI/AttackPossibility.cpp
+++ b/AI/BattleAI/AttackPossibility.cpp
@@ -12,6 +12,10 @@
 #include "../../lib/CStack.h" // TODO: remove
                               // Eventually only IBattleInfoCallback and battle::Unit should be used, 
                               // CUnitState should be private and CStack should be removed completely
+#include "../../lib/spells/CSpellHandler.h"
+#include "../../lib/spells/ISpellMechanics.h"
+#include "../../lib/spells/ObstacleCasterProxy.h"
+#include "../../lib/battle/CObstacleInstance.h"
 
 uint64_t averageDmg(const DamageRange & range)
 {
@@ -25,9 +29,57 @@ void DamageCache::cacheDamage(const battle::Unit * attacker, const battle::Unit
 	damageCache[attacker->unitId()][defender->unitId()] = static_cast<float>(damage) / attacker->getCount();
 }
 
+void DamageCache::buildObstacleDamageCache(std::shared_ptr<HypotheticBattle> hb, BattleSide side)
+{
+	for(const auto & obst : hb->battleGetAllObstacles(side))
+	{
+		auto spellObstacle = dynamic_cast<const SpellCreatedObstacle *>(obst.get());
+
+		if(!spellObstacle || !obst->triggersEffects())
+			continue;
+
+		auto triggerAbility = VLC->spells()->getById(obst->getTrigger());
+		auto triggerIsNegative = triggerAbility->isNegative() || triggerAbility->isDamage();
+
+		if(!triggerIsNegative)
+			continue;
+
+		const auto * hero = hb->battleGetFightingHero(spellObstacle->casterSide);
+		auto caster = spells::ObstacleCasterProxy(hb->getSidePlayer(spellObstacle->casterSide), hero, *spellObstacle);
+
+		auto affectedHexes = obst->getAffectedTiles();
+		auto stacks = hb->battleGetUnitsIf([](const battle::Unit * u) -> bool {
+			return u->alive() && !u->isTurret() && u->getPosition().isValid();
+		});
+
+		for(auto stack : stacks)
+		{
+			std::shared_ptr<HypotheticBattle> inner = std::make_shared<HypotheticBattle>(hb->env, hb);
+			auto cast = spells::BattleCast(hb.get(), &caster, spells::Mode::PASSIVE, obst->getTrigger().toSpell());
+			auto updated = inner->getForUpdate(stack->unitId());
+
+			spells::Target target;
+			target.push_back(spells::Destination(updated.get()));
+
+			cast.castEval(inner->getServerCallback(), target);
+
+			auto damageDealt = stack->getAvailableHealth() - updated->getAvailableHealth();
+
+			for(auto hex : affectedHexes)
+			{
+				obstacleDamage[hex][stack->unitId()] = damageDealt;
+			}
+		}
+	}
+}
 
 void DamageCache::buildDamageCache(std::shared_ptr<HypotheticBattle> hb, BattleSide side)
 {
+	if(parent == nullptr)
+	{
+		buildObstacleDamageCache(hb, side);
+	}
+
 	auto stacks = hb->battleGetUnitsIf([=](const battle::Unit * u) -> bool
 		{
 			return u->isValidTarget();
@@ -70,6 +122,23 @@ int64_t DamageCache::getDamage(const battle::Unit * attacker, const battle::Unit
 	return damageCache[attacker->unitId()][defender->unitId()] * attacker->getCount();
 }
 
+int64_t DamageCache::getObstacleDamage(BattleHex hex, const battle::Unit * defender)
+{
+	if(parent)
+		return parent->getObstacleDamage(hex, defender);
+
+	auto damages = obstacleDamage.find(hex);
+
+	if(damages == obstacleDamage.end())
+		return 0;
+
+	auto damage = damages->second.find(defender->unitId());
+
+	return damage == damages->second.end()
+		? 0
+		: damage->second;
+}
+
 int64_t DamageCache::getOriginalDamage(const battle::Unit * attacker, const battle::Unit * defender, std::shared_ptr<CBattleInfoCallback> hb)
 {
 	if(parent)
@@ -288,6 +357,15 @@ AttackPossibility AttackPossibility::evaluate(
 			{
 				retaliatedUnits.push_back(attacker);
 			}
+
+			auto obstacleDamage = damageCache.getObstacleDamage(hex, attacker);
+
+			if(obstacleDamage > 0)
+			{
+				ap.attackerDamageReduce += calculateDamageReduce(nullptr, attacker, obstacleDamage, damageCache, state);
+
+				ap.attackerState->damage(obstacleDamage);
+			}
 		}
 
 		// ensure the defender is also affected
diff --git a/AI/BattleAI/AttackPossibility.h b/AI/BattleAI/AttackPossibility.h
index 990dcdb00..3ef8e1523 100644
--- a/AI/BattleAI/AttackPossibility.h
+++ b/AI/BattleAI/AttackPossibility.h
@@ -18,14 +18,18 @@ class DamageCache
 {
 private:
 	std::unordered_map<uint32_t, std::unordered_map<uint32_t, float>> damageCache;
+	std::map<BattleHex, std::unordered_map<uint32_t, int64_t>> obstacleDamage;
 	DamageCache * parent;
 
+	void buildObstacleDamageCache(std::shared_ptr<HypotheticBattle> hb, BattleSide side);
+
 public:
 	DamageCache() : parent(nullptr) {}
 	DamageCache(DamageCache * parent) : parent(parent) {}
 
 	void cacheDamage(const battle::Unit * attacker, const battle::Unit * defender, std::shared_ptr<CBattleInfoCallback> hb);
 	int64_t getDamage(const battle::Unit * attacker, const battle::Unit * defender, std::shared_ptr<CBattleInfoCallback> hb);
+	int64_t getObstacleDamage(BattleHex hex, const battle::Unit * defender);
 	int64_t getOriginalDamage(const battle::Unit * attacker, const battle::Unit * defender, std::shared_ptr<CBattleInfoCallback> hb);
 	void buildDamageCache(std::shared_ptr<HypotheticBattle> hb, BattleSide side);
 };
diff --git a/AI/BattleAI/BattleEvaluator.cpp b/AI/BattleAI/BattleEvaluator.cpp
index 8ee042f14..555865619 100644
--- a/AI/BattleAI/BattleEvaluator.cpp
+++ b/AI/BattleAI/BattleEvaluator.cpp
@@ -226,11 +226,36 @@ BattleAction BattleEvaluator::selectStackAction(const CStack * stack)
 					{
 						return BattleAction::makeDefend(stack);
 					}
-					else
+
+					auto enemyMellee = hb->getUnitsIf([this](const battle::Unit * u) -> bool
+						{
+							return u->unitSide() == BattleSide::ATTACKER && !hb->battleCanShoot(u);
+						});
+
+					bool isTargetOutsideFort = bestAttack.dest.getY() < GameConstants::BFIELD_WIDTH - 4;
+					bool siegeDefense = stack->unitSide() == BattleSide::DEFENDER
+						&& !bestAttack.attack.shooting
+						&& hb->battleGetFortifications().hasMoat
+						&& !enemyMellee.empty()
+						&& isTargetOutsideFort;
+
+					if(siegeDefense)
 					{
-						activeActionMade = true;
-						return BattleAction::makeMeleeAttack(stack, bestAttack.attack.defenderPos, bestAttack.from);
+						logAi->trace("Evaluating exchange at %d self-defense", stack->getPosition().hex);
+
+						BattleAttackInfo bai(stack, stack, 0, false);
+						AttackPossibility apDefend(stack->getPosition(), stack->getPosition(), bai);
+
+						float defenseValue = scoreEvaluator.evaluateExchange(apDefend, 0, *targets, damageCache, hb);
+
+						if((defenseValue > score && score <= 0) || (defenseValue > 2 * score && score > 0))
+						{
+							return BattleAction::makeDefend(stack);
+						}
 					}
+					
+					activeActionMade = true;
+					return BattleAction::makeMeleeAttack(stack, bestAttack.attack.defenderPos, bestAttack.from);
 				}
 			}
 		}
diff --git a/AI/BattleAI/BattleExchangeVariant.cpp b/AI/BattleAI/BattleExchangeVariant.cpp
index 70c881d23..8726fda7e 100644
--- a/AI/BattleAI/BattleExchangeVariant.cpp
+++ b/AI/BattleAI/BattleExchangeVariant.cpp
@@ -28,6 +28,12 @@ float BattleExchangeVariant::trackAttack(
 	std::shared_ptr<HypotheticBattle> hb,
 	DamageCache & damageCache)
 {
+	if(!ap.attackerState)
+	{
+		logAi->trace("Skipping fake ap attack");
+		return 0;
+	}
+
 	auto attacker = hb->getForUpdate(ap.attack.attacker->unitId());
 
 	float attackValue = ap.attackValue();
@@ -485,15 +491,18 @@ ReachabilityData BattleExchangeEvaluator::getExchangeUnits(
 		vstd::concatenate(allReachableUnits, turn == 0 ? reachabilityMap.at(hex) : getOneTurnReachableUnits(turn, hex));
 	}
 
-	for(auto hex : ap.attack.attacker->getHexes())
+	if(!ap.attack.attacker->isTurret())
 	{
-		auto unitsReachingAttacker = turn == 0 ? reachabilityMap.at(hex) : getOneTurnReachableUnits(turn, hex);
-		for(auto unit : unitsReachingAttacker)
+		for(auto hex : ap.attack.attacker->getHexes())
 		{
-			if(unit->unitSide() != ap.attack.attacker->unitSide())
+			auto unitsReachingAttacker = turn == 0 ? reachabilityMap.at(hex) : getOneTurnReachableUnits(turn, hex);
+			for(auto unit : unitsReachingAttacker)
 			{
-				allReachableUnits.push_back(unit);
-				result.enemyUnitsReachingAttacker.insert(unit->unitId());
+				if(unit->unitSide() != ap.attack.attacker->unitSide())
+				{
+					allReachableUnits.push_back(unit);
+					result.enemyUnitsReachingAttacker.insert(unit->unitId());
+				}
 			}
 		}
 	}
diff --git a/AI/BattleAI/PotentialTargets.cpp b/AI/BattleAI/PotentialTargets.cpp
index a341921e6..f38415ef7 100644
--- a/AI/BattleAI/PotentialTargets.cpp
+++ b/AI/BattleAI/PotentialTargets.cpp
@@ -10,6 +10,7 @@
 #include "StdInc.h"
 #include "PotentialTargets.h"
 #include "../../lib/CStack.h"//todo: remove
+#include "../../lib/mapObjects/CGTownInstance.h"
 
 PotentialTargets::PotentialTargets(
 	const battle::Unit * attacker,
diff --git a/AI/Nullkiller/Goals/RecruitHero.cpp b/AI/Nullkiller/Goals/RecruitHero.cpp
index c6a6c4d4e..02a333b7d 100644
--- a/AI/Nullkiller/Goals/RecruitHero.cpp
+++ b/AI/Nullkiller/Goals/RecruitHero.cpp
@@ -68,7 +68,12 @@ void RecruitHero::accept(AIGateway * ai)
 		throw cannotFulfillGoalException("Town " + t->nodeName() + " is occupied. Cannot recruit hero!");
 
 	cb->recruitHero(t, heroToHire);
-	ai->nullkiller->heroManager->update();
+
+	{
+		std::unique_lock lockGuard(ai->nullkiller->aiStateMutex);
+
+		ai->nullkiller->heroManager->update();
+	}
 
 	if(t->visitingHero)
 		ai->moveHeroToTile(t->visitablePos(), t->visitingHero.get());