In the northern part of the inclosure, not far from the north-western angle, Sir Henry Layard made some excavations that brought one of the principal gates of ancient Nineveh to light.[79] The passage was probably vaulted, but its upper part had disappeared. The gateway, which was built by Sennacherib, had a pair of winged bulls looking towards the city and another pair looking towards the country outside. The limestone pavement in the entrance still bears the mark of wheels. Two great chambers are hollowed out of the thickness of the walls and open into the entrance passage. The walls must be here about 116 feet thick, judging from the proportion, in Layard’s plan,[80] between them and one of the two chambers, which has a diameter, as we are told by its finder, of 23 feet. We need say no more of this doorway. The town attached to the palace of Khorsabad will give us a better opportunity for the study of a city gate. The “town of Sargon,” _Dour-Saryoukin_ or _Hisr-Sargon_, according as we follow one or the other method of transcribing the Assyrian name, was far smaller than Babylon, was smaller even than Nineveh. It formed a parallelogram two sides of which were about 1,950 yards, the other two about 1,870 yards long, which would give a surface of considerably more than a square mile. This city is interesting not for the part it played in history, for of that we know nothing, and it is quite possible that after the death of Sargon it may have been practically abandoned, but because, of all the cities of Assyria, it is that whose line of circumvallation has been best preserved and most carefully studied (Vol. I. Fig. 144). Like all inhabited places of any importance Dour-Saryoukin was carefully fortified. Over the whole of Mesopotamia the words town and fortress seem to have been almost convertible terms. The nature of the soil does not lend itself to any such distinctions as those of upper and lower city, as it does in Italy and Greece; there was no _acropolis_, to which the inhabitants could fly when the outer defences were broken down. In case of great need the royal palace with its massive gates and cincture of commanding towers might be looked upon as a citadel; while in Babylon and some other towns several concentric lines of fortification made an attack more arduous and prolonged the defence. But, nevertheless, the chief care of the Mesopotamian engineers was given to the strengthening of the external wall, the _enceinte_, properly speaking.