The Southern Wall is in length, and which the historian Josephus equates as being equal to the length of one furlong (Greek: stadion). Herod's southern extension of the Temple Mount is clearly visible from the east, standing on the Mount of Olives or to a visitor standing on top of the Temple mount as a slight change in the plane of the eastern wall, the so-called Straight Joint. Herod's Royal Stoa stood atop this southern extension. The retaining wall is built of enormous blocks of Jerusalem stone, the face of each ashlar (block) is edged with a margin, the bossage is raised about 3/8 above the surrounding margins. The unmortared blocks are so finely fitted together that a knife blade cannot be inserted between the ashlars.