The building is rather like a medieval Castle and was established in the Sixth Century and soon afterwards, as the Moslem armies advanced Westwards from the Arabian Peninsula, somebody had the prescience to build a small Mosque in its courtyard to guard against it being burned or demolished. At the time of the Crusades it was the turn of the Monastery to protect the Mosque, and so it has been down the ages, each House of God extending its shelter to the other as opposing armies came and went.