warfare gained during the Crusades. A slight retrospect, under these conditions, is desirable, which will give us some insight into the methods of siegecraft during the period of whose strongholds and art of fortification we already have seen something. Many classical texts, from the time of Cæsar to the latest days of the western Empire, supply us with authority for Roman military methods. No passage throws fuller light on their siege practice than Cæsar’s description of his siege of Alesia in Burgundy, the hill fortress occupied by Vercingetorix.[65] The lines which were first drawn round the stronghold by Cæsar were eleven miles in circuit, and communicated with three camps, on hills of a height equal to that of the hill of Alesia. Along the lines there were twenty-three _castella_, small forts to hold pickets, and temporary examples of the type of which the “mile-castles” of the Roman wall were permanent instances. The stubborn resistance of Vercingetorix and the prospect of the arrival of a relieving army, however, gave Cæsar occasion to elaborate his lines, the character of which is very minutely described. They consisted of an earthen bank with a ditch 20 feet broad, 400 feet in front of it on the side towards the besieged stronghold. The ditch was dug with perpendicular sides: its distance from the bank was a precaution against sudden attacks of the enemy, and placed the bank out of the range of casual missiles. The space between the bank and ditch was not a level “berm,” but was furrowed by two ditches, 15 feet in breadth and depth, of which the inner was wet, the water of the neighbouring streams being diverted into it. Behind the inner ditch rose the earthen _agger_ or bank, to the height of 12 feet. The _vallum_, the rampart on the top of the _agger_, was of a type common in early warfare and for many centuries later, consisting of a breastwork of interlaced twigs stiffened by a row of palisades. The hurdles of the breastwork were finished off with battlement-like projections: at intervals there were tall uprights with forked tops, which were called _cervi_ or “stags,” and acted as _chevaux-de-frise_ along the whole rampart. There were also towers, obviously temporary constructions of timber, at distances of 80 feet from one another. This, however, was not enough. Cæsar aimed at holding his lines with as few men as possible, so as to allow the rest to do the necessary foraging at a distance. He therefore proceeded to sow the approach to the lines with pitfalls. Five ditches, 5 feet deep, were dug out and filled with upright stakes sharpened to a point and fastened together at the bottom by continuous cross pieces. In front of these were three rows of pits, 3 feet deep, arranged in a series of _quincunces_ or saltires: in these were placed smooth sharpened stakes, so that little more than their points stuck out of the ground, and the pits were then covered over with twigs and brushwood.