diff --git a/src/matrix/room/persister.js b/src/matrix/room/persister.js
index c08fbc92..6ed72ece 100644
--- a/src/matrix/room/persister.js
+++ b/src/matrix/room/persister.js
@@ -17,9 +17,9 @@ export default class RoomPersister {
 		}
 	}
 
-	// async persistGapFill(...) {
-
-	// }
+	async persistGapFill(gapEntry, response) {
+        throw new Error("not yet implemented");
+	}
 
 	persistSync(roomResponse, txn) {
 		let nextKey = this._lastSortKey;
diff --git a/src/matrix/room/room.js b/src/matrix/room/room.js
index a581fbcb..014ea529 100644
--- a/src/matrix/room/room.js
+++ b/src/matrix/room/room.js
@@ -4,10 +4,11 @@ import RoomPersister from "./persister.js";
 import Timeline from "./timeline.js";
 
 export default class Room extends EventEmitter {
-	constructor(roomId, storage, emitCollectionChange) {
+	constructor({roomId, storage, hsApi, emitCollectionChange}) {
         super();
-		this._roomId = roomId;
-		this._storage = storage;
+        this._roomId = roomId;
+        this._storage = storage;
+        this._hsApi = hsApi;
 		this._summary = new RoomSummary(roomId);
 		this._persister = new RoomPersister(roomId);
         this._emitCollectionChange = emitCollectionChange;
@@ -50,6 +51,8 @@ export default class Room extends EventEmitter {
         this._timeline = new Timeline({
             roomId: this.id,
             storage: this._storage,
+            persister: this._persister,
+            hsApi: this._hsApi,
             closeCallback: () => this._timeline = null,
         });
         await this._timeline.load();
diff --git a/src/matrix/room/timeline.js b/src/matrix/room/timeline.js
index 44f5f83d..27abee37 100644
--- a/src/matrix/room/timeline.js
+++ b/src/matrix/room/timeline.js
@@ -24,6 +24,30 @@ export default class Timeline {
         }
     }
 
+    /** @public */
+    async fillGap(gapEntry, amount) {
+        const gap = gapEntry.gap;
+        let direction;
+        if (gap.prev_batch) {
+            direction = "b";
+        } else if (gap.next_batch) {
+            direction = "f";
+        } else {
+            throw new Error("Invalid gap, no prev_batch or next_batch field: " + JSON.stringify(gapEntry.gap));
+        }
+        const token = gap.prev_batch || gap.next_batch;
+
+        const response = await this._hsApi.messages({
+            roomId: this._roomId,
+            from: token,
+            dir: direction,
+            limit: amount
+        });
+        const newEntries = await this._persister.persistGapFill(gapEntry, response);
+        // find where to replace existing gap with newEntries by doing binary search
+
+    }
+
     /** @public */
     get entries() {
         return this._entriesList;
diff --git a/src/matrix/session.js b/src/matrix/session.js
index 1f9a3d7e..9dbeb010 100644
--- a/src/matrix/session.js
+++ b/src/matrix/session.js
@@ -2,8 +2,10 @@ import Room from "./room/room.js";
 import { ObservableMap } from "../observable/index.js";
 
 export default class Session {
-	constructor({storage, sessionInfo}) {
+    // sessionInfo contains deviceId, userId and homeServer
+	constructor({storage, hsApi, sessionInfo}) {
 		this._storage = storage;
+        this._hsApi = hsApi;
 		this._session = null;
         this._sessionInfo = sessionInfo;
 		this._rooms = new ObservableMap();
@@ -36,7 +38,12 @@ export default class Session {
     }
 
 	createRoom(roomId) {
-		const room = new Room(roomId, this._storage, this._roomUpdateCallback);
+		const room = new Room({
+            roomId,
+            storage: this._storage,
+            emitCollectionChange: this._roomUpdateCallback,
+            hsApi: this._hsApi,
+        });
 		this._rooms.add(roomId, room);
 		return room;
 	}