Rejoining the Wall, Haltwhistle-burn-head is the first object of interest that we meet with in our course westward. The burn, to which important reference will presently be made, is derived from the overflowings of Greenlee-lough. Between its source, and the gap by which it passes the ridge on which the Wall stands, it is called the Caw-burn; below that point it bears the name of Haltwhistle-burn. As the width of the defile, and the passage of the stream, render this a weak point in the barrier, the two lines of fortification approach very near to each other; they afterwards again diverge. Westward of Burn-head farm-house, the fosse is boldly developed, but the Wall is traceable only in the ruins of its foundation. As we proceed onwards to Great Chesters, the foundations of a mile-castle which has stood half to the north of the Wall, and half within it, may be, though not without careful scrutiny, observed. The tower which formerly stood at Portgate is the only other known example of a similar arrangement. [Sidenote: GREAT CHESTERS.] ÆSICA, or Great Chesters, is the tenth stationary camp on the line of the Wall. Its superficial contents are 3 acres, 35 poles. The ramparts and fosse are clearly defined. The southern gateway may be traced; it is nearer the eastern than the western side. A double rampart of earth seems to have given additional security to the western side, which, by situation, is the weakest. A vaulted room in the centre of the camp still answers very correctly to the description given of it in 1800 by Dr. Lingard, (quoted by Hodgson, II. iii. 203.) It is 6½ feet square, and 5 feet high. It was descended by steps, and had, at the opposite end to its entrance, a sort of bench, raised on mason work, 2½ feet wide and high, and covered with a slab of stone. The roof consisted of six similar and contiguous arches of stone, each 15 inches broad. It had also one pillar. The floor had on it a great quantity of ashes, was flagged, and on raising one of the stones, a spring gushed out, which converted the vault into a well. About one hundred and fifty yards south of the station, in a field which has for years been furrowed by the plough, the remains of a building of somewhat rude construction have just been discovered. Its floor, consisting, for the most part, of the usual compost, is nearly a foot thick. Further examination would probably disclose, in its vicinity, the foundations of numerous suburban buildings. An ancient road leads from the southern gateway of the station to the great military way which ran from CILURNUM to MAGNA. [Sidenote: ÆSICA.]