To these two co-operating forces--legions and auxiliaries--we must add the Imperial Guards, twelve regiments of 1000 men each, quartered in Italy, and generally congregated in a special camp just outside the gate at the top of the Quirinal and Viminal Hills beyond the modern railway station. Like other Guards, these were a picked body, containing many volunteers from Italy itself, while others came from the most romanized parts of Gaul or elsewhere. They enjoyed many privileges, wore a more gorgeous armour, served only sixteen years and received double pay. Frequently it came to be the case that this particular body of troops was the one which made and unmade emperors, chiefly under the influence of pecuniary promises or largess. Besides these, 6000 City Guards were in barracks inside the metropolis for the protection of the town; 7000 _gendarmerie_, already mentioned, served as night-watch and fire-brigade, but perhaps scarcely rank as soldiers. Here and there in the empire there also existed separate volunteer detachments of various dimensions serving on special duty, and it was to one of these that belonged the Cornelius of the Acts of the Apostles, who is there described as a centurion of the "Italian band." [Illustration: FIG. 106.--BESIEGERS WITH THE "TORTOISE."] It would carry us too far afield if we entered into detailed descriptions of Roman warfare--of Roman marches, Roman camps, and fortifications, Roman sieges, and military engines. Otherwise it would be highly interesting to watch the attack made upon an enemy's wall or gate by a band of men pushing in front of them a wicker screen covered with hide, or holding their shields locked together above their heads, so as to form a roof to shelter them from the spears, stones, firebrands, and pots of flame which rained down from the walls. [Illustration: FIG 107.--ROMAN ARTILLERY.]