From the church-yard wall, all along the edge of the _mesilla_, descending into the depression mentioned, and again rounding the highest northern point, then crossing over transversely from west to east and running back south along the opposite edge, there extends a wall of circumvallation, constructed, as far as may be seen, of rubble and broken stones, with occasional earth flung in between the blocks. This wall has, along its periphery, a total length of 983 m.--3,220 ft.--according to Mr. Thurston's measurement.[99] It was, as far as can be seen, 2 m.--6 ft. 6 in.--high on an average, and about 0.50 m.--20 in.--thick. There is but one entrance to it visible, on the west side, at its lowest level, where the depression already mentioned runs down the slope to the south-west as the bed of a rocky streamlet. There a gateway of 4 m.--13 ft.--in width is left open; the wall itself thickens on each side to a round tower built of stones, mixed with earthy fillings. These towers, considerably ruined, are still 2 m.--6 ft. 6 in.--high, and appear to have been at least 4m.--13 ft.--in diameter; at all events the northern one. At the gateway itself the walls curve outward,[100] and appear to have terminated in a short passage of entering and re-entering lines, between which there was a passage, as well for man as for the waters from the _mesilla_ into the bottom and the stream below. But these lines can only be surmised from the streaks of gravel and stones extending beyond the gateway, as no definite foundations are extant. Pl. I., Fig. 3, is a tolerably correct diagram of this gateway. [Illustration: PLATE IX VIEW OF GATEWAY OF CIRCUMVALLATION, FROM THE EAST.] The face of the wall at each side of the gate is 1.3 m.--4 ft.--wide. Whether there was any contrivance to close it or not it is now impossible to determine; but there are in the northern wall of the gate pieces of decayed wood embedded in and protruding from the stone-work. For what purpose they were placed there it is not permitted even to conjecture. * * * * * Having thus sketched, as far as I am able, the topography of the _mesilla_, and described its great wall of circumvallation, I now turn to the ruins which cover its upper surface, starting for their survey from the transverse wall of the old church-yard, 10 m.--33 ft.--north of the church, and proceeding thence northward along the top of the tabulated bluff.[101]