The lofty granite wall which surrounded the entire enclosure was pierced by but a single gate which opened opposite the east end of the palace. This gate was large and of massive construction, appearing to have been built to withstand the assault of numerous and well-armed forces. So strong did it appear that the ape-man could not but harbor the opinion that it had been constructed to protect the interior against forces equipped with heavy battering rams. That such a force had ever existed within the vicinity in historic times seemed most unlikely, and Tarzan conjectured, therefore, that the wall and the gate were of almost unthinkable antiquity, dating, doubtless, from the forgotten age of the Atlantians, and constructed, perhaps, to protect the builders of the Palace of Diamonds from the well-armed forces that had come from Atlantis to work the gold mines of Opar and to colonize central Africa. While the wall, the gate, and the palace itself, suggested in many ways almost unbelievable age, yet they were in such an excellent state of repair that it was evident that they were still inhabited by rational and intelligent creatures; while upon the south side Tarzan had seen a new tower in process of construction, where a number of blacks working under the direction of Bolgani were cutting and shaping granite blocks and putting them in place. Tarzan had halted in a tree near the east gate to watch the life passing in and out of the palace grounds beneath the ancient portal, and as he watched, a long cavalcade of powerful Gomangani emerged from the forest and entered the enclosure. Swung in hides between two poles, this party was carrying rough-hewn blocks of granite, four men to a block. Two or three Bolgani accompanied the long line of carriers, which was preceded and followed by a detachment of black warriors, armed with battle-axes and spears. The demeanor and attitude of the black porters, as well as of the Bolgani, suggested to the ape-man nothing more nor less than a caravan of donkeys, plodding their stupid way at the behest of their drivers. If one lagged he was prodded with the point of a spear or struck with its haft. There was no greater brutality shown than in the ordinary handling of beasts of burden the world around, nor in the demeanor of the blacks was there any more indication of objection or revolt than you see depicted upon the faces of a long line of burden-bearing mules; to all intents and purposes they were dumb, driven cattle. Slowly they filed through the gateway and disappeared from sight.