The Mount of Olives is actually a small mountain chain, east of Jerusalem. The Garden of Gethsemane was at the foot of the mountain. Jesus and his followers retreated there a few times.
The story of the Agony in the Garden is told (differently) in three gospels: Matthew 26:36-56, Mark 14:32-52 and Luke 22:39-53. In John 18:1-12 only the episode of the arrest is told, which followed the prayer.
Related works of art:
Bellini, Giovanni: Agony in the Garden (c. 1465)
Borgianni, Orazio: Agony in the Garden (1610)
Duccio: Prayer on the Mount of Olives (Maestà ) (1308-11)
Goya, Francisco: Christ on the Mount of Olives (1819)
Mantegna, Andrea: Agony in the Garden (San Zeno) (1457-1459)
Mantegna, Andrea: The Agony in the Garden (c. 1455)