John 18:2

‘Now Judas also, who betrayed him, knew the place, for Jesus often went there with his disciples.'

This important piece of information explains why Judas was able to find him so easily and why he was needed in order to obtain the arrest. They had tried to arrest Jesus in official places when people were present and had been unable to do so. Judas provided them with the opportunity of finding Him comparatively alone in a private and secluded place.

The fact that this was a regular rendezvous ties in with Luke 21:37 where we are told that Jesus taught in the Temple by day, and by night would go to the Mount of Olives. It is quite possible that some provision of accommodation was made for Him there. Alternately they may have slept in the open air or in tents.