Damascus has many historical sites dating back to many different periods of the city's history. Since the city has been built up with every passing job, it has become almost impossible to dig out all the ruins of Damascus that lie up to 8 feet (2.4 m) below the modern level. The Citadel of Damascus is located in the northwest corner of the Old City. The Bab Sharqi street is filled with small shops and leads to the old Christian quarter of Bab Tuma (St. Thomas's Gate). Medhat Pasha Souq is also a main market in Damascus and was named after Medhat Pasha. At the end of the Bab Sharqi street, one reaches the House of Ananias, an underground chapel that was the cellar of Ananias's house. The Umayyad Mosque, also known as the Grand Mosque of Damascus, is one of the largest mosques in the world and also one of the oldest sites of continuous prayer since the rise of Islam.