The Coenaculum is the traditional place for the "upper room" where the Last Supper was held. The crusaders, being literalists, made sure their chapel was on the second-storey of the building and "David's tomb" was subsequently installed below. It is also associated with the room belonging to John Mark's mother in which the disciples were baptised in the Holy Spirit, but this again is difficult to verify.
In 1335, 80 years after the collapse of the crusader kingdom, the Franciscans who had remained at their posts as Custodians of the Holy Land bought the site from the Caliphate. They were involved in an argument with the Jews over David's tomb in the 15th century, only solved by the Muslims taking charge and turning all of it into a mosque in 1551. Today Christians and Jews still share the building
Luke Chapter 22
7 Then came the day of Unleavened Bread, on which the passover lamb had to be sacrificed. 8 So Jesus sent Peter and John, saying, “Go and prepare the passover for us, that we may eat it.” 9 They said to him, “Where will you have us prepare it?” 10 He said to them, “Behold, when you have entered the city, a man carrying a jar of water will meet you; follow him into the house which he enters, 11 and tell the householder, ‘The Teacher says to you, Where is the guest room, where I am to eat the passover with my disciples?’ 12 And he will show you a large upper room furnished; there make ready.” 13 And they went, and found it as he had told them; and they prepared the passover.
14 And when the hour came, he sat at table, and the apostles with him. 15 And he said to them, “I have earnestly desired to eat this passover with you before I suffer; 16 for I tell you I shall not eat it until it is fulfilled in the kingdom of God.” 17 And he took a cup, and when he had given thanks he said, “Take this, and divide it among yourselves; 18 for I tell you that from now on I shall not drink of the fruit of the vine until the kingdom of God comes.” 19 And he took bread, and when he had given thanks he broke it and gave it to them, saying, “This is my body which is given for you. Do this in remembrance of me.” 20 And likewise the cup after supper, saying, “This cup which is poured out for you is the new covenant in my blood. 21 But behold the hand of him who betrays me is with me on the table. 22 For the Son of man goes as it has been determined; but woe to that man by whom he is betrayed!” 23 And they began to question one another, which of them it was that would do this.
The Revised Standard Version, (New York: Oxford University Press, Inc.) 1973, 1977.