9 And whence has the Saviour risen? He says in the Song of Songs: Rise up, come, My neighbour: and in what follows, in a cave of the rock! A cave of the rock He called the cave which was erewhile before the door of the Saviour's sepulchre, and had been hewn out of the rock itself, as is wont to be done here in front of the sepulchres. For now it is not to be seen, since the outer cave was cut away at that time for the sake of the present adornment. For before the decoration of the sepulchre by the royal munificence, there was a cave in the front of the rock. But where is the rock that had in it the cave? Does it lie near the middle of the city, or near the walls and the outskirts? And whether is it within the ancient walls, or within the outer walls which were built afterwards? He says then in the Canticles: in a cave of the rock, close to the outer wall.
Source: Catechetical Lectures (New Advent)