The present room of the Last Supper and location of the Pentecost can not be this room built only in the 12th century. Yet the present location that could be near the original place mentioned in the Gospels, has provided a place to commemorate the scriptures for thousands of pilgrims whom have traveled to the Holy Land of Israel for centuries.
Some believe that the “little Church of God” mentioned by Epiphanius of Salamis on Mount Zion was on this very site, which perhaps a wealthy Christian of this time opened his home to be used as a church. Later on the 4th century after Christian persecution ended, a Church was constructed here on Mount Zion, at which point it was known as “the Upper Church of the Apostles,” named after the occurrence of the Pentecost, the receiving of the Holy Spirit (Acts 1:13, 2:1).
Later in the 5th century the churched was renamed to "Zion, Mother of all the Churches," and it was around this period that it was traditionally identified as the site of the Last Supper. The natural conclusion seems to come about that since both the Pentecost and Last Supper occurred in the same location, the two events must have been in the same room.
The present church standing today and the Upper room pilgrim’s visit today on holy land tours was built by the Crusaders in the 12th Century as part of the Church of St. Mary of Zion, having found the Byzantine church in ruins in 614, and in 965 from two Persian attacks. After this time the Crusader church became a glorious pilgrim Jerusalem site, but it fell in ruins yet again after the Crusaders were defeated, only to have the remains pillaged for building materials.
The site was reconstructed again and restored by Franciscans in the fourteen century and used as a Franciscan monastery until 1552, and even though in 1524 the Ottoman Empire transformed the room in to a mosque, they were more concerned with the Tomb of King David, which to Muslim tradition is the “Prophet David,” then the Upper Room. Today the site is no longer a mosque and the building of the Crusaders remains.
You’ll find on your holy land tour in Israel an attractive Last Supper Room with classic Crusader arches and pillars, and a mostly empty room. There are still remnants of the 14th century paint on the wall inside to the right of the room, the chamber with it’s mosque trappings including restored stained-glass Ottoman windows with Arabic inscriptions and the ornate mihrab (an alcove indicating the direction of Mecca). There is also two Arabic plaques in the wall and a Levantine dome.
Stairs in the south-west end corner of the room lead down to the Tomb of King David. A dome above the stairs is supported by marble columns with adorned pelicans pecking their parent's breast, a symbol of sacrifice and charity in Christianity. Stairs by the minaret lead-up to the roof top, from where there are beautiful views to the Mount of Olives and Jerusalem.