diff --git a/libs/util/include/psemek/util/ecs.hpp b/libs/util/include/psemek/util/ecs.hpp
index 43908af0..1f2a69c8 100644
--- a/libs/util/include/psemek/util/ecs.hpp
+++ b/libs/util/include/psemek/util/ecs.hpp
@@ -10,6 +10,7 @@
 #include <memory>
 #include <string>
 #include <string_view>
+#include <functional>
 
 #include <experimental/type_traits>
 
@@ -19,11 +20,43 @@ namespace psemek::util
 	namespace ecs_detail
 	{
 
-		using handle = std::uint32_t;
+		using species_handle = std::uint16_t;
+
+		// Entity id within it's species
+		using entity_id = std::uint32_t;
+
+		using entity_version = std::uint32_t;
+
+		// From highest to lowest bits:
+		//    12: species id
+		//    20: entity id (within species)
+		//    32: entity version
+		using entity_handle = std::uint64_t;
+
+		struct unpacked_handle
+		{
+			species_handle species;
+			entity_id entity;
+			entity_version version;
+		};
+
+		inline unpacked_handle unpack(entity_handle h)
+		{
+			return {
+				h >> 52,
+				(h >> 32) & 0xFFFFFu,
+				h & 0xFFFFFFFFu
+			};
+		}
+
+		inline entity_handle pack(species_handle species, entity_id id, entity_version version)
+		{
+			return (static_cast<entity_handle>(species) << 52) | (static_cast<entity_handle>(id) << 32) | static_cast<entity_handle>(version);
+		}
 
 		struct species_base
 		{
-			species_base(std::string name, handle id)
+			species_base(std::string name, species_handle id)
 				: name_(std::move(name))
 				, id_(id)
 			{}
@@ -45,15 +78,12 @@ namespace psemek::util
 				return reinterpret_cast<typename Component::data *>(get_entity_component(typeid(Component)));
 			}
 
-			virtual handle entity_count() const = 0;
+			virtual entity_id entity_count() const = 0;
 
-			virtual handle add_entity() = 0;
-			virtual void remove_entity(handle h) = 0;
+			virtual entity_handle add_entity() = 0;
+			virtual void remove_entity(entity_handle h) = 0;
 
-			bool entity_active(handle h)
-			{
-				return get_free_list()[h] == h;
-			}
+			virtual bool entity_active(entity_handle h) const = 0;
 
 			template <typename Behavior>
 			void apply(Behavior & behavior)
@@ -63,12 +93,14 @@ namespace psemek::util
 
 			virtual ~species_base() {}
 
-			virtual handle const * get_free_list() = 0;
-			virtual std::size_t list_size() const = 0;
+			virtual entity_id const * get_free_list() const = 0;
+			virtual entity_id list_size() const = 0;
 
-		private:
+			virtual entity_version const * get_version_list() const = 0;
+
+		protected:
 			std::string name_;
-			handle id_;
+			species_handle id_;
 
 			template <typename Behavior, typename ... Components, std::size_t ... Is>
 			void apply_impl(Behavior & behavior, std::tuple<Components...> *, std::index_sequence<Is...>)
@@ -86,8 +118,6 @@ namespace psemek::util
 					return;
 
 				typename Behavior::context ctx;
-				ctx.species = id_;
-				ctx.species_name = name_;
 
 				((std::get<Components *>(ctx.components) = get_species_component<Components>()), ...);
 
@@ -113,19 +143,21 @@ namespace psemek::util
 				if (list)
 				{
 					// sparse
-					std::size_t const size = list_size();
-					for (std::size_t i = 0; i < size; ++i)
+					auto const size = list_size();
+					auto version = get_version_list();
+					for (entity_id i = 0; i < size; ++i)
 					{
 						if (*list == i)
 						{
-							ctx.entity = i;
+							ctx.entity.value = pack(id_, i, *version);
 							ctx.remove = false;
 							std::apply(visit, cptrs);
 							if (ctx.remove)
-								remove_entity(i);
+								remove_entity(ctx.entity.value);
 						}
 						std::apply(increment, cptrs);
 						++list;
+						++version;
 					}
 				}
 				else
@@ -133,11 +165,11 @@ namespace psemek::util
 					// packed
 					for (std::size_t i = 0; i < entity_count();)
 					{
-						ctx.entity = i;
+						ctx.entity.value = pack(id_, i, 0);
 						ctx.remove = false;
 						std::apply(visit, cptrs);
 						if (ctx.remove)
-							remove_entity(i);
+							remove_entity(ctx.entity.value);
 						else
 						{
 							std::apply(increment, cptrs);
@@ -152,7 +184,7 @@ namespace psemek::util
 		struct species_impl_base
 			: species_base
 		{
-			species_impl_base(std::string name, handle id, Components && ... components)
+			species_impl_base(std::string name, species_handle id, Components && ... components)
 				: species_base(std::move(name), id)
 				, species_components_{std::move(components)...}
 			{}
@@ -199,42 +231,58 @@ namespace psemek::util
 		{
 			using species_impl_base<Components...>::species_impl_base;
 
-			static constexpr handle null = static_cast<handle>(-1);
+			static constexpr entity_id null = static_cast<entity_id>(-1);
 
-			handle entity_count() const override
+			entity_id entity_count() const override
 			{
 				return entity_count_;
 			}
 
-			handle add_entity() override
+			entity_handle add_entity() override
 			{
 				return add_entity_impl(std::make_index_sequence<sizeof...(Components)>{});
 			}
 
-			void remove_entity(handle h) override
+			void remove_entity(entity_handle h) override
 			{
-				list_[h] = list_head_;
-				list_head_ = h;
+				auto id = unpack(h).entity;
+				list_[id] = list_head_;
+				list_head_ = id;
+				destroyed_at_[id] = ++version_;
 				--entity_count_;
 			}
 
-			handle const * get_free_list() override
+			bool entity_active(entity_handle h) const override
+			{
+				auto u = unpack(h);
+				return list_[u.entity] == u.entity && u.version >= destroyed_at_[u.entity];
+			}
+
+			entity_id const * get_free_list() const override
 			{
 				return list_.data();
 			}
 
-			std::size_t list_size() const override
+			entity_id list_size() const override
 			{
 				return list_.size();
 			}
 
+			entity_version const * get_version_list() const override
+			{
+				return created_at_.data();
+			}
+
 		private:
-			std::vector<handle> list_;
-			handle list_head_ = null;
-			std::size_t entity_count_ = 0;
+			std::vector<entity_id> list_;
+			entity_id list_head_ = null;
+			entity_id entity_count_ = 0;
+			std::vector<entity_version> created_at_;
+			std::vector<entity_version> destroyed_at_;
+			entity_version version_ = 0;
 
 			template <std::size_t ... I>
-			handle add_entity_impl(std::index_sequence<I...>)
+			entity_handle add_entity_impl(std::index_sequence<I...>)
 			{
 				if (list_head_ == null)
 				{
@@ -242,6 +290,8 @@ namespace psemek::util
 					std::size_t const new_size = std::max<std::size_t>(16, old_size * 2);
 
 					list_.resize(new_size);
+					created_at_.resize(new_size, 0);
+					destroyed_at_.resize(new_size, 0);
 					for (std::size_t i = old_size; i + 1 < new_size; ++i)
 						list_[i] = i + 1;
 					list_[new_size - 1] = null;
@@ -250,14 +300,15 @@ namespace psemek::util
 					((std::get<I>(this->entity_components_).resize(new_size)), ...);
 				}
 
-				auto result = list_head_;
+				auto id = list_head_;
 
-				((std::get<I>(this->entity_components_)[result] = {}), ...);
+				((std::get<I>(this->entity_components_)[id] = {}), ...);
 
 				list_head_ = list_[list_head_];
-				list_[result] = result;
+				list_[id] = id;
 				entity_count_++;
-				return result;
+				created_at_[id] = version_;
+				return pack(this->id_, id, version_);
 			}
 		};
 
@@ -267,47 +318,58 @@ namespace psemek::util
 		{
 			using species_impl_base<Components...>::species_impl_base;
 
-			handle entity_count() const override
+			entity_id entity_count() const override
 			{
 				return std::get<0>(this->entity_components_).size();
 			}
 
-			handle add_entity() override
+			entity_handle add_entity() override
 			{
 				return add_entity_impl(std::make_index_sequence<sizeof...(Components)>{});
 			}
 
-			void remove_entity(handle h) override
+			void remove_entity(entity_handle h) override
 			{
 				remove_entity_impl(h, std::make_index_sequence<sizeof...(Components)>{});
 			}
 
-			handle const * get_free_list() override
+			bool entity_active(entity_handle h) const override
+			{
+				return unpack(h).entity < entity_count();
+			}
+
+			entity_id const * get_free_list() const override
 			{
 				return nullptr;
 			}
 
-			std::size_t list_size() const override
+			entity_id list_size() const override
 			{
 				return 0;
 			}
 
+			entity_version const * get_version_list() const override
+			{
+				return nullptr;
+			}
+
 		private:
 
 			template <std::size_t ... I>
-			handle add_entity_impl(std::index_sequence<I...>)
+			entity_handle add_entity_impl(std::index_sequence<I...>)
 			{
-				handle result = entity_count();
+				entity_id id = entity_count();
 				((std::get<I>(this->entity_components_).emplace_back()), ...);
-				return result;
+				return pack(this->id_, id, 0);
 			}
 
 			template <std::size_t ... I>
-			void remove_entity_impl(handle h, std::index_sequence<I...>)
+			void remove_entity_impl(entity_handle h, std::index_sequence<I...>)
 			{
-				if (h + 1 != entity_count())
+				auto u = unpack(h);
+				if (u.entity + 1 != entity_count())
 				{
-					(std::swap(std::get<I>(this->entity_components_)[h], std::get<I>(this->entity_components_).back()), ...);
+					(std::swap(std::get<I>(this->entity_components_)[u.entity], std::get<I>(this->entity_components_).back()), ...);
 				}
 
 				((std::get<I>(this->entity_components_).pop_back()), ...);
@@ -318,6 +380,20 @@ namespace psemek::util
 
 	struct ecs
 	{
+		struct species_handle
+		{
+			ecs_detail::species_handle value;
+
+			friend auto operator <=> (species_handle const &, species_handle const &) = default;
+		};
+
+		struct entity_handle
+		{
+			ecs_detail::entity_handle value;
+
+			friend auto operator <=> (entity_handle const &, entity_handle const &) = default;
+		};
+
 		template <typename ... Components>
 		struct behavior
 		{
@@ -326,9 +402,7 @@ namespace psemek::util
 
 			struct context
 			{
-				ecs_detail::handle species;
-				std::string_view species_name;
-				ecs_detail::handle entity;
+				entity_handle entity;
 
 				component_ptrs components;
 
@@ -342,8 +416,6 @@ namespace psemek::util
 			};
 		};
 
-		using handle = ecs_detail::handle;
-
 		enum class policy
 		{
 			sparse,
@@ -351,139 +423,141 @@ namespace psemek::util
 		};
 
 		template <typename ... Components>
-		handle register_species(std::string name, policy p, Components && ... components);
+		species_handle register_species(std::string name, policy p, Components && ... components);
 
-		handle species_count() const { return species_.size(); }
+		ecs_detail::species_handle species_count() const { return species_.size(); }
 
-		std::string_view species_name(handle species) const { return species_[species]->name(); }
+		std::string_view species_name(species_handle species) const { return species_[species.value]->name(); }
 
-		handle add_entity(handle species);
-		handle entity_count(handle species) const;
-		void remove_entity(handle species, handle entity);
-		bool entity_active(handle species, handle entity);
+		species_handle entity_species(entity_handle entity) const { return {ecs_detail::unpack(entity.value).species}; }
 
-		handle capacity(handle species) const { return species_[species]->list_size(); }
+		entity_handle add_entity(species_handle species);
+		ecs_detail::entity_id entity_count(species_handle species) const;
+		void remove_entity(entity_handle entity);
+		bool entity_active(entity_handle entity);
 
 		template <typename Component>
-		Component & get(handle species);
+		Component & get(species_handle species);
 
 		template <typename Component>
-		Component const & get(handle species) const;
+		Component const & get(species_handle species) const;
 
 		template <typename Component>
-		typename Component::data & get(handle species, handle entity);
+		typename Component::data & get(entity_handle entity);
 
 		template <typename Component>
-		typename Component::data const & get(handle species, handle entity) const;
+		typename Component::data const & get(entity_handle entity) const;
 
 		template <typename Component>
-		Component * get_if(handle species);
+		Component * get_if(species_handle species);
 
 		template <typename Component>
-		Component const * get_if(handle species) const;
+		Component const * get_if(species_handle species) const;
 
 		template <typename Component>
-		typename Component::data * get_if(handle species, handle entity);
+		typename Component::data * get_if(entity_handle entity);
 
 		template <typename Component>
-		typename Component::data const * get_if(handle species, handle entity) const;
+		typename Component::data const * get_if(entity_handle entity) const;
 
 		template <typename Behavior>
 		void apply(Behavior && behavior);
 
 		template <typename Behavior>
-		void apply(Behavior && behavior, handle species);
+		void apply(Behavior && behavior, species_handle species);
 
 	private:
 		std::vector<std::unique_ptr<ecs_detail::species_base>> species_;
 	};
 
 	template <typename ... Components>
-	ecs::handle ecs::register_species(std::string name, policy p, Components && ... components)
+	ecs::species_handle ecs::register_species(std::string name, policy p, Components && ... components)
 	{
-		handle result = species_.size();
+		auto result = species_count();
 		if (p == policy::sparse)
 			species_.push_back(std::make_unique<ecs_detail::sparse_species_impl<Components...>>(std::move(name), result, std::move(components)...));
 		else
 			species_.push_back(std::make_unique<ecs_detail::packed_species_impl<Components...>>(std::move(name), result, std::move(components)...));
-		return result;
+		return {result};
 	}
 
-	inline ecs::handle ecs::add_entity(handle species)
+	inline ecs::entity_handle ecs::add_entity(species_handle species)
 	{
-		return species_[species]->add_entity();
+		return {species_[species.value]->add_entity()};
 	}
 
-	inline ecs::handle ecs::entity_count(handle species) const
+	inline ecs_detail::entity_id ecs::entity_count(species_handle species) const
 	{
-		return species_[species]->entity_count();
+		return species_[species.value]->entity_count();
 	}
 
-	inline void ecs::remove_entity(handle species, handle entity)
+	inline void ecs::remove_entity(entity_handle entity)
 	{
-		species_[species]->remove_entity(entity);
+		species_[ecs_detail::unpack(entity.value).species]->remove_entity(entity.value);
 	}
 
-	inline bool ecs::entity_active(handle species, handle entity)
+	inline bool ecs::entity_active(entity_handle entity)
 	{
-		return species_[species]->entity_active(entity);
+		return species_[ecs_detail::unpack(entity.value).species]->entity_active(entity.value);
 	}
 
 	template <typename Component>
-	Component & ecs::get(handle species)
+	Component & ecs::get(species_handle species)
 	{
-		auto p = species_[species]->get_species_component<Component>();
+		auto p = species_[species.value]->get_species_component<Component>();
 		if (!p)
-			throw std::runtime_error(util::to_string("Component ", type_name<Component>(), " is not present in species ", species_[species]->name()));
+			throw std::runtime_error(util::to_string("Component ", type_name<Component>(), " is not present in species ", species_[species.value]->name()));
 		return *p;
 	}
 
 	template <typename Component>
-	Component const & ecs::get(handle species) const
+	Component const & ecs::get(species_handle species) const
 	{
 		return const_cast<Component const &>(const_cast<ecs *>(this)->get<Component>(species));
 	}
 
 	template <typename Component>
-	typename Component::data & ecs::get(handle species, handle entity)
+	typename Component::data & ecs::get(entity_handle entity)
 	{
-		auto p = species_[species]->get_entity_component<Component>();
+		auto u = ecs_detail::unpack(entity.value);
+		auto p = species_[u.species]->get_entity_component<Component>();
 		if (!p)
-			throw std::runtime_error(util::to_string("Component ", type_name<Component>(), " is not present in species ", species_[species]->name()));
-		return p[entity];
+			throw std::runtime_error(util::to_string("Component ", type_name<Component>(), " is not present in species ", species_[u.species]->name()));
+		return p[u.entity];
 	}
 
 	template <typename Component>
-	typename Component::data const & ecs::get(handle species, handle entity) const
+	typename Component::data const & ecs::get(entity_handle entity) const
 	{
-		return const_cast<typename Component::data const &>(const_cast<ecs *>(this)->get<Component>(species, entity));
+		return const_cast<typename Component::data const &>(const_cast<ecs *>(this)->get<Component>(entity));
 	}
 
 	template <typename Component>
-	Component * ecs::get_if(handle species)
+	Component * ecs::get_if(species_handle species)
 	{
-		return species_[species]->get_species_component<Component>();
+		return species_[species.value]->get_species_component<Component>();
 	}
 
 	template <typename Component>
-	Component const * ecs::get_if(handle species) const
+	Component const * ecs::get_if(species_handle species) const
 	{
 		return const_cast<typename Component::data const *>(const_cast<ecs *>(this)->get<Component>(species));
 	}
 
 	template <typename Component>
-	typename Component::data * ecs::get_if(handle species, handle entity)
+	typename Component::data * ecs::get_if(entity_handle entity)
 	{
-		auto p = species_[species]->get_entity_component<Component>();
+		auto u = ecs_detail::unpack(entity.value);
+		auto p = species_[u.species]->get_entity_component<Component>();
 		if (p)
-			return p + entity;
+			return p + u.entity;
 		return p;
 	}
 
 	template <typename Component>
-	typename Component::data const * ecs::get_if(handle species, handle entity) const
+	typename Component::data const * ecs::get_if(entity_handle entity) const
 	{
-		return const_cast<typename Component::data const *>(const_cast<ecs *>(this)->get_if<Component>(species, entity));
+		return const_cast<typename Component::data const *>(const_cast<ecs *>(this)->get_if<Component>(entity));
 	}
 
 	template <typename Behavior>
@@ -494,9 +568,32 @@ namespace psemek::util
 	}
 
 	template <typename Behavior>
-	void ecs::apply(Behavior && behavior, handle species)
+	void ecs::apply(Behavior && behavior, species_handle species)
 	{
-		species_[species]->apply(behavior);
+		species_[species.value]->apply(behavior);
 	}
 
 }
+
+namespace std
+{
+
+	template <>
+	struct hash<::psemek::util::ecs::species_handle>
+	{
+		std::size_t operator()(::psemek::util::ecs::species_handle h) const
+		{
+			return std::hash<::psemek::util::ecs_detail::species_handle>()(h.value);
+		}
+	};
+
+	template <>
+	struct hash<::psemek::util::ecs::entity_handle>
+	{
+		std::size_t operator()(::psemek::util::ecs::entity_handle h) const
+		{
+			return std::hash<::psemek::util::ecs_detail::entity_handle>()(h.value);
+		}
+	};
+
+}