"Then they returned to Jerusalem from the hill called the Mount of Olives, a Sabbath days walk from the city. When they arrived, they went upstairs to the room where they were staying." (Acts 1:12-13)
The building identified as the Coenaculum or the Cenacle is a small, two-storey structure within a larger complex of buildings on the summit of Mount Zion. The upper storey was built by the Franciscans in the 14th century to commemorate the Last Supper. It is also identified as the "upper room" in which the Holy Spirit descended upon the Disciples at Pentecost (Acts 2:2-3). In Christian tradition, the area of the city in which they were living at the time was the present Mount Zion (the geographical name somehow having been transferred from the Temple Mount to this hill in the southwest corner of the city possibly through a 4th-century misreading of Micah 3:12, which seems to speak of two hills: "the Mountain of the Lord and Zion").
The ground-floor room beneath the Coenaculum contains a cenotaph that since the 12th century has been known as the "tomb of King David" - even though the recorded burial place of the king was in the "City of David" on the Ophel Ridge (1 Kings 2:10). Beneath the level of the present floor are earlier Crusader, Byzantine and Roman foundations. An apse behind the cenotaph is aligned with the Temple Mount, leading to speculation that this part of the building may have been a synagogue, or even "the synagogue" mentioned by the Pilgrim of Bordeaux in 333.
This area of the hill became part of the Mother Church of Holy Zion (shown in the 6th-century mosaic Madaba Map). This basilica was destroyed by the Persians in 614. The 12th-century Crusader Monastery and Church of St. Mary were built on the foundations of this earlier church, but in 1219 it too was destroyed (probably in the demolition of the walls and strongpoints around the city ordered by the Ayyubid Sultan Al-Muazzam).
The present Chapel of the Coenaculum was built by the Franciscans on their return to the city in 1335. The ribbed vaulting of the ceiling is typical of Lusignan or Cypriot Gothic. The sculpted mihrab, the Muslim prayer niche, was added in 1523, when the Franciscans were evicted from the building and the room converted into a mosque.
Sources: Israeli Foreign Ministry