diff --git a/lib/matrix_server.ex b/lib/matrix_server.ex
index 53213d3..7acc43d 100644
--- a/lib/matrix_server.ex
+++ b/lib/matrix_server.ex
@@ -31,4 +31,20 @@ defmodule MatrixServer do
   end
 
   def default_room_version, do: "7"
+
+  def get_domain(id) do
+    case String.split(id, ":") do
+      [_, server_name] -> server_name
+      _ -> nil
+    end
+  end
+
+  # https://elixirforum.com/t/22709/9
+  def has_duplicates?(list) do
+    list
+    |> Enum.reduce_while(%MapSet{}, fn x, acc ->
+      if MapSet.member?(acc, x), do: {:halt, false}, else: {:cont, MapSet.put(acc, x)}
+    end)
+    |> is_boolean()
+  end
 end
diff --git a/lib/matrix_server/event.ex b/lib/matrix_server/event.ex
index d59e8a9..df0473b 100644
--- a/lib/matrix_server/event.ex
+++ b/lib/matrix_server/event.ex
@@ -1,9 +1,9 @@
 defmodule MatrixServer.Event do
   use Ecto.Schema
 
-  import Ecto.Changeset
+  import Ecto.Query
 
-  alias MatrixServer.{Room, Event}
+  alias MatrixServer.{Repo, Room, Event}
 
   @primary_key {:event_id, :string, []}
   schema "events" do
@@ -17,12 +17,6 @@ defmodule MatrixServer.Event do
     belongs_to :room, Room, type: :string
   end
 
-  def changeset(event, params \\ %{}) do
-    event
-    |> cast(params, [:type, :timestamp, :state_key, :sender, :content])
-    |> validate_required([:type, :timestamp, :sender])
-  end
-
   def new(room_id, sender) do
     %Event{
       room_id: room_id,
@@ -122,4 +116,110 @@ defmodule MatrixServer.Event do
   def is_control_event(_), do: false
 
   def is_state_event(%Event{state_key: state_key}), do: state_key != nil
+
+  # Perform validations that can be done before state resolution.
+  # For example checking the domain of the sender.
+  # We assume that required keys, as well as in the content, is already validated.
+
+  # Rule 1.4 is left to changeset validation.
+  def prevalidate(%Event{
+        type: "m.room.create",
+        prev_events: prev_events,
+        auth_events: auth_events,
+        room_id: room_id,
+        sender: sender
+      }) do
+    # TODO: error check on domains?
+    # TODO: rule 1.3
+
+    # Check rules: 1.1, 1.2
+    prev_events == [] and
+      auth_events == [] and
+      MatrixServer.get_domain(sender) == MatrixServer.get_domain(room_id)
+  end
+
+  def prevalidate(%Event{auth_events: auth_event_ids, prev_events: prev_event_ids} = event) do
+    prev_events =
+      Event
+      |> where([e], e.event_id in ^prev_event_ids)
+      |> Repo.all()
+
+    auth_events =
+      Event
+      |> where([e], e.event_id in ^auth_event_ids)
+      |> Repo.all()
+
+    state_pairs = Enum.map(auth_events, &{&1.type, &1.state_key})
+
+    # Check rules: 2.1, 2.2, 3
+    length(auth_events) == length(auth_event_ids) and
+      length(prev_events) == length(prev_event_ids) and
+      not MatrixServer.has_duplicates?(state_pairs) and
+      valid_auth_events?(event, auth_events) and
+      Enum.find_value(state_pairs, &(&1 == {"m.room.create", ""})) and
+      do_prevalidate(event, auth_events, prev_events)
+  end
+
+  # Rule 4.1 is left to changeset validation.
+  defp do_prevalidate(%Event{type: "m.room.aliases", sender: sender, state_key: state_key}, _, _) do
+    # Check rule: 4.2
+    MatrixServer.get_domain(sender) == MatrixServer.get_domain(state_key)
+  end
+
+  # Rule 5.1 is left to changeset validation.
+  # Rules 5.2.3, 5.2.4, 5.2.5 is left to state resolution.
+  # Check rule: 5.2.1
+  defp do_prevalidate(
+         %Event{type: "m.room.member", content: %{"membership" => "join"}, sender: sender},
+         _,
+         [%Event{type: "m.room.create", state_key: sender}]
+       ),
+       do: true
+
+  # Check rule: 5.2.2
+  defp do_prevalidate(
+         %Event{
+           type: "m.room.member",
+           content: %{"membership" => "join"},
+           sender: sender,
+           state_key: state_key
+         },
+         _,
+         _
+       )
+       when sender != state_key,
+       do: false
+
+  # TODO: Rule 5.3.1
+  # All other rules will be checked during state resolution.
+  defp do_prevalidate(_, _, _), do: true
+
+  defp valid_auth_events?(
+         %Event{type: type, sender: sender, state_key: state_key, content: content},
+         auth_events
+       ) do
+    Enum.all?(auth_events, fn
+      %Event{type: "m.room.create", state_key: ""} ->
+        true
+
+      %Event{type: "m.room.power_levels", state_key: ""} ->
+        true
+
+      %Event{type: "m.room.member", state_key: ^sender} ->
+        true
+
+      %Event{type: auth_type, state_key: auth_state_key} ->
+        if type == "m.room.member" do
+          %{"membership" => membership} = content
+
+          (auth_type == "m.room.member" and auth_state_key == state_key) or
+            (membership in ["join", "invite"] and auth_type == "m.room.join_rules" and
+               auth_state_key == "") or
+            (membership == "invite" and auth_type == "m.room.third_party_invite" and
+               auth_state_key == "")
+        else
+          false
+        end
+    end)
+  end
 end
diff --git a/lib/matrix_server/room.ex b/lib/matrix_server/room.ex
index 767abba..9d23993 100644
--- a/lib/matrix_server/room.ex
+++ b/lib/matrix_server/room.ex
@@ -27,7 +27,7 @@ defmodule MatrixServer.Room do
   end
 
   def generate_room_id do
-    "!" <> MatrixServer.random_string(18) <> "@" <> MatrixServer.server_name()
+    "!" <> MatrixServer.random_string(18) <> ":" <> MatrixServer.server_name()
   end
 
   def update_forward_extremities(%Event{
diff --git a/lib/matrix_server/room_server.ex b/lib/matrix_server/room_server.ex
index f88708a..cba4cd7 100644
--- a/lib/matrix_server/room_server.ex
+++ b/lib/matrix_server/room_server.ex
@@ -38,8 +38,16 @@ defmodule MatrixServer.RoomServer do
     Repo.transaction(fn ->
       with {:ok, create_room_event, state_set} <-
              room_creation_create_room(account, input, room, state_set),
-           {:ok, _join_creator_event, state_set} <-
-             room_creation_join_creator(account, room, state_set, create_room_event) do
+           {:ok, join_creator_event, state_set} <-
+             room_creation_join_creator(account, room, state_set, create_room_event),
+           {:ok, _power_levels_event, state_set} <-
+             room_creation_power_levels(
+               account,
+               room,
+               state_set,
+               create_room_event,
+               join_creator_event
+             ) do
         {:ok, %{room_id: room_id, state_set: state_set}}
       else
         _ -> {:error, :something}
@@ -61,11 +69,24 @@ defmodule MatrixServer.RoomServer do
          %Account{localpart: localpart},
          %Room{id: room_id},
          state_set,
-         %Event{event_id: create_room_event_id}
+         %Event{event_id: create_room_id}
        ) do
     Event.join(room_id, MatrixServer.get_mxid(localpart))
-    |> Map.put(:auth_events, [create_room_event_id])
-    |> Map.put(:prev_events, [create_room_event_id])
+    |> Map.put(:auth_events, [create_room_id])
+    |> Map.put(:prev_events, [create_room_id])
+    |> verify_and_insert_event(state_set)
+  end
+
+  defp room_creation_power_levels(
+         %Account{localpart: localpart},
+         %Room{id: room_id},
+         state_set,
+         %Event{event_id: create_room_id},
+         %Event{event_id: join_creator_id}
+       ) do
+    Event.power_levels(room_id, MatrixServer.get_mxid(localpart))
+    |> Map.put(:auth_events, [create_room_id, join_creator_id])
+    |> Map.put(:prev_events, [join_creator_id])
     |> verify_and_insert_event(state_set)
   end
 
@@ -77,24 +98,28 @@ defmodule MatrixServer.RoomServer do
     # 4. Passes authorization rules based on the event's auth events, otherwise it is rejected.
     # 5. Passes authorization rules based on the state at the event, otherwise it is rejected.
     # 6. Passes authorization rules based on the current state of the room, otherwise it is "soft failed".
-    if StateResolution.is_authorized_by_auth_events(event) do
-      state_set = StateResolution.resolve(event, false)
+    if Event.prevalidate(event) do
+      if StateResolution.is_authorized_by_auth_events(event) do
+        state_set = StateResolution.resolve(event, false)
 
-      if StateResolution.is_authorized(event, state_set) do
-        if StateResolution.is_authorized(event, current_state_set) do
-          # TODO: Assume the event is a forward extremity, should check this actually.
-          Room.update_forward_extremities(event)
-          {:ok, event} = Repo.insert(event)
-          state_set = StateResolution.resolve_forward_extremities(event)
-          {:ok, event, state_set}
+        if StateResolution.is_authorized(event, state_set) do
+          if StateResolution.is_authorized(event, current_state_set) do
+            # We assume here that the event is always a forward extremity.
+            Room.update_forward_extremities(event)
+            {:ok, event} = Repo.insert(event)
+            state_set = StateResolution.resolve_forward_extremities(event)
+            {:ok, event, state_set}
+          else
+            {:error, :soft_failed}
+          end
         else
-          {:error, :soft_failed}
+          {:error, :rejected}
         end
       else
         {:error, :rejected}
       end
     else
-      {:error, :rejected}
+      {:error, :invalid}
     end
   end