diff --git a/changelog.d/6820.misc b/changelog.d/6820.misc
new file mode 100644
index 000000000..08aa80bcd
--- /dev/null
+++ b/changelog.d/6820.misc
@@ -0,0 +1 @@
+Refactoring work in preparation for changing the event redaction algorithm.
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index 1c9456e58..0c2060160 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -402,11 +402,9 @@ class UnsupportedRoomVersionError(SynapseError):
     """The client's request to create a room used a room version that the server does
     not support."""
 
-    def __init__(self):
+    def __init__(self, msg="Homeserver does not support this room version"):
         super(UnsupportedRoomVersionError, self).__init__(
-            code=400,
-            msg="Homeserver does not support this room version",
-            errcode=Codes.UNSUPPORTED_ROOM_VERSION,
+            code=400, msg=msg, errcode=Codes.UNSUPPORTED_ROOM_VERSION,
         )
 
 
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index d57e8ca7a..4ac3d81cb 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -198,7 +198,7 @@ class FederationClient(FederationBase):
 
         logger.debug("backfill transaction_data=%r", transaction_data)
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
         format_ver = room_version_to_event_format(room_version)
 
         pdus = [
@@ -336,7 +336,7 @@ class FederationClient(FederationBase):
     def get_event_auth(self, destination, room_id, event_id):
         res = yield self.transport_layer.get_event_auth(destination, room_id, event_id)
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
         format_ver = room_version_to_event_format(room_version)
 
         auth_chain = [
@@ -649,7 +649,7 @@ class FederationClient(FederationBase):
 
     @defer.inlineCallbacks
     def send_invite(self, destination, room_id, event_id, pdu):
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
 
         content = yield self._do_send_invite(destination, pdu, room_version)
 
@@ -657,7 +657,7 @@ class FederationClient(FederationBase):
 
         logger.debug("Got response to send_invite: %s", pdu_dict)
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
         format_ver = room_version_to_event_format(room_version)
 
         pdu = event_from_pdu_json(pdu_dict, format_ver)
@@ -859,7 +859,7 @@ class FederationClient(FederationBase):
                 timeout=timeout,
             )
 
-            room_version = yield self.store.get_room_version(room_id)
+            room_version = yield self.store.get_room_version_id(room_id)
             format_ver = room_version_to_event_format(room_version)
 
             events = [
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 9562faa3e..a4c97ed45 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -234,7 +234,7 @@ class FederationServer(FederationBase):
                 continue
 
             try:
-                room_version = await self.store.get_room_version(room_id)
+                room_version = await self.store.get_room_version_id(room_id)
             except NotFoundError:
                 logger.info("Ignoring PDU for unknown room_id: %s", room_id)
                 continue
@@ -334,7 +334,7 @@ class FederationServer(FederationBase):
                 )
             )
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
         resp["room_version"] = room_version
 
         return 200, resp
@@ -385,7 +385,7 @@ class FederationServer(FederationBase):
         origin_host, _ = parse_server_name(origin)
         await self.check_server_matches_acl(origin_host, room_id)
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
         if room_version not in supported_versions:
             logger.warning(
                 "Room version %s not in %s", room_version, supported_versions
@@ -417,7 +417,7 @@ class FederationServer(FederationBase):
     async def on_send_join_request(self, origin, content, room_id):
         logger.debug("on_send_join_request: content: %s", content)
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
         format_ver = room_version_to_event_format(room_version)
         pdu = event_from_pdu_json(content, format_ver)
 
@@ -440,7 +440,7 @@ class FederationServer(FederationBase):
         await self.check_server_matches_acl(origin_host, room_id)
         pdu = await self.handler.on_make_leave_request(origin, room_id, user_id)
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
 
         time_now = self._clock.time_msec()
         return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
@@ -448,7 +448,7 @@ class FederationServer(FederationBase):
     async def on_send_leave_request(self, origin, content, room_id):
         logger.debug("on_send_leave_request: content: %s", content)
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
         format_ver = room_version_to_event_format(room_version)
         pdu = event_from_pdu_json(content, format_ver)
 
@@ -495,7 +495,7 @@ class FederationServer(FederationBase):
             origin_host, _ = parse_server_name(origin)
             await self.check_server_matches_acl(origin_host, room_id)
 
-            room_version = await self.store.get_room_version(room_id)
+            room_version = await self.store.get_room_version_id(room_id)
             format_ver = room_version_to_event_format(room_version)
 
             auth_chain = [
@@ -664,7 +664,7 @@ class FederationServer(FederationBase):
                 logger.info("Accepting join PDU %s from %s", pdu.event_id, origin)
 
         # We've already checked that we know the room version by this point
-        room_version = await self.store.get_room_version(pdu.room_id)
+        room_version = await self.store.get_room_version_id(pdu.room_id)
 
         # Check signature.
         try:
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 1f92640f8..0f10c3e9b 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -388,7 +388,7 @@ class FederationHandler(BaseHandler):
                             for x in remote_state:
                                 event_map[x.event_id] = x
 
-                    room_version = await self.store.get_room_version(room_id)
+                    room_version = await self.store.get_room_version_id(room_id)
                     state_map = await resolve_events_with_store(
                         room_id,
                         room_version,
@@ -1110,7 +1110,7 @@ class FederationHandler(BaseHandler):
         Logs a warning if we can't find the given event.
         """
 
-        room_version = await self.store.get_room_version(room_id)
+        room_version = await self.store.get_room_version_id(room_id)
 
         event_infos = []
 
@@ -1373,7 +1373,7 @@ class FederationHandler(BaseHandler):
 
         event_content = {"membership": Membership.JOIN}
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
 
         builder = self.event_builder_factory.new(
             room_version,
@@ -1607,7 +1607,7 @@ class FederationHandler(BaseHandler):
             )
             raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
         builder = self.event_builder_factory.new(
             room_version,
             {
@@ -2059,7 +2059,7 @@ class FederationHandler(BaseHandler):
                 do_soft_fail_check = False
 
         if do_soft_fail_check:
-            room_version = yield self.store.get_room_version(event.room_id)
+            room_version = yield self.store.get_room_version_id(event.room_id)
             room_version_obj = KNOWN_ROOM_VERSIONS[room_version]
 
             # Calculate the "current state".
@@ -2195,7 +2195,7 @@ class FederationHandler(BaseHandler):
         Returns:
             defer.Deferred[EventContext]: updated context object
         """
-        room_version = yield self.store.get_room_version(event.room_id)
+        room_version = yield self.store.get_room_version_id(event.room_id)
         room_version_obj = KNOWN_ROOM_VERSIONS[room_version]
 
         try:
@@ -2367,7 +2367,7 @@ class FederationHandler(BaseHandler):
         remote_auth_events.update({(d.type, d.state_key): d for d in different_events})
         remote_state = remote_auth_events.values()
 
-        room_version = yield self.store.get_room_version(event.room_id)
+        room_version = yield self.store.get_room_version_id(event.room_id)
         new_state = yield self.state_handler.resolve_events(
             room_version, (local_state, remote_state), event
         )
@@ -2591,7 +2591,7 @@ class FederationHandler(BaseHandler):
         }
 
         if (yield self.auth.check_host_in_room(room_id, self.hs.hostname)):
-            room_version = yield self.store.get_room_version(room_id)
+            room_version = yield self.store.get_room_version_id(room_id)
             builder = self.event_builder_factory.new(room_version, event_dict)
 
             EventValidator().validate_builder(builder)
@@ -2654,7 +2654,7 @@ class FederationHandler(BaseHandler):
         Returns:
             Deferred: resolves (to None)
         """
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
 
         # NB: event_dict has a particular specced format we might need to fudge
         # if we change event formats too much.
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 9a0f661b9..bdf16c84d 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -459,7 +459,9 @@ class EventCreationHandler(object):
             room_version = event_dict["content"]["room_version"]
         else:
             try:
-                room_version = yield self.store.get_room_version(event_dict["room_id"])
+                room_version = yield self.store.get_room_version_id(
+                    event_dict["room_id"]
+                )
             except NotFoundError:
                 raise AuthError(403, "Unknown room")
 
@@ -788,7 +790,7 @@ class EventCreationHandler(object):
         ):
             room_version = event.content.get("room_version", RoomVersions.V1.identifier)
         else:
-            room_version = yield self.store.get_room_version(event.room_id)
+            room_version = yield self.store.get_room_version_id(event.room_id)
 
         event_allowed = yield self.third_party_event_rules.check_event_allowed(
             event, context
@@ -963,7 +965,7 @@ class EventCreationHandler(object):
             auth_events = yield self.store.get_events(auth_events_ids)
             auth_events = {(e.type, e.state_key): e for e in auth_events.values()}
 
-            room_version = yield self.store.get_room_version(event.room_id)
+            room_version = yield self.store.get_room_version_id(event.room_id)
             room_version_obj = KNOWN_ROOM_VERSIONS[room_version]
 
             if event_auth.check_redaction(
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index 71d76202c..caf841a64 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -281,7 +281,7 @@ class PaginationHandler(object):
         """Purge the given room from the database"""
         with (await self.pagination_lock.write(room_id)):
             # check we know about the room
-            await self.store.get_room_version(room_id)
+            await self.store.get_room_version_id(room_id)
 
             # first check that we have no users in this room
             joined = await defer.maybeDeferred(
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index a95b45d79..138239955 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -178,7 +178,7 @@ class RoomCreationHandler(BaseHandler):
             },
             token_id=requester.access_token_id,
         )
-        old_room_version = yield self.store.get_room_version(old_room_id)
+        old_room_version = yield self.store.get_room_version_id(old_room_id)
         yield self.auth.check_from_context(
             old_room_version, tombstone_event, tombstone_context
         )
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index cacd0c0c2..fdd6bef6b 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -394,7 +394,7 @@ class StateHandler(object):
                 delta_ids=delta_ids,
             )
 
-        room_version = yield self.store.get_room_version(room_id)
+        room_version = yield self.store.get_room_version_id(room_id)
 
         result = yield self._state_resolution_handler.resolve_state_groups(
             room_id,
diff --git a/synapse/storage/data_stores/main/state.py b/synapse/storage/data_stores/main/state.py
index 4167f83c9..3d34103e6 100644
--- a/synapse/storage/data_stores/main/state.py
+++ b/synapse/storage/data_stores/main/state.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -22,7 +23,8 @@ from six import iteritems
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
-from synapse.api.errors import NotFoundError
+from synapse.api.errors import NotFoundError, UnsupportedRoomVersionError
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.storage._base import SQLBaseStore
@@ -61,8 +63,29 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
     def __init__(self, database: Database, db_conn, hs):
         super(StateGroupWorkerStore, self).__init__(database, db_conn, hs)
 
+    async def get_room_version(self, room_id: str) -> RoomVersion:
+        """Get the room_version of a given room
+
+        Raises:
+            NotFoundError: if the room is unknown
+
+            UnsupportedRoomVersionError: if the room uses an unknown room version.
+                Typically this happens if support for the room's version has been
+                removed from Synapse.
+        """
+        room_version_id = await self.get_room_version_id(room_id)
+        v = KNOWN_ROOM_VERSIONS.get(room_version_id)
+
+        if not v:
+            raise UnsupportedRoomVersionError(
+                "Room %s uses a room version %s which is no longer supported"
+                % (room_id, room_version_id)
+            )
+
+        return v
+
     @cached(max_entries=10000)
-    async def get_room_version(self, room_id: str) -> str:
+    async def get_room_version_id(self, room_id: str) -> str:
         """Get the room_version of a given room
 
         Raises:
diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py
index 86166fd4c..af3fd67ab 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -661,7 +661,7 @@ class EventsPersistenceStorage(object):
                 break
 
         if not room_version:
-            room_version = await self.main_store.get_room_version(room_id)
+            room_version = await self.main_store.get_room_version_id(room_id)
 
         logger.debug("calling resolve_state_groups from preserve_events")
         res = await self._state_resolution_handler.resolve_state_groups(
diff --git a/tests/handlers/test_presence.py b/tests/handlers/test_presence.py
index d4293b431..e92e090c3 100644
--- a/tests/handlers/test_presence.py
+++ b/tests/handlers/test_presence.py
@@ -588,7 +588,7 @@ class PresenceJoinTestCase(unittest.HomeserverTestCase):
 
         hostname = get_domain_from_id(user_id)
 
-        room_version = self.get_success(self.store.get_room_version(room_id))
+        room_version = self.get_success(self.store.get_room_version_id(room_id))
 
         builder = EventBuilder(
             state=self.state,
diff --git a/tests/test_state.py b/tests/test_state.py
index e0aae06be..1e4449fa1 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -119,7 +119,7 @@ class StateGroupStore(object):
     def register_event_id_state_group(self, event_id, state_group):
         self._event_to_state_group[event_id] = state_group
 
-    def get_room_version(self, room_id):
+    def get_room_version_id(self, room_id):
         return RoomVersions.V1.identifier
 
 
diff --git a/tests/unittest.py b/tests/unittest.py
index b56e24938..98bf27d39 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -589,7 +589,9 @@ class HomeserverTestCase(TestCase):
         event_builder_factory = self.hs.get_event_builder_factory()
         event_creation_handler = self.hs.get_event_creation_handler()
 
-        room_version = self.get_success(self.hs.get_datastore().get_room_version(room))
+        room_version = self.get_success(
+            self.hs.get_datastore().get_room_version_id(room)
+        )
 
         builder = event_builder_factory.for_room_version(
             KNOWN_ROOM_VERSIONS[room_version],