It is difficult to fix any precise date to these buildings, but we may perhaps conclude, with some appearance of reason, that the greater number of them were erected by the Romans under the emperors, who possessed, at various times, the whole of the north coast of Africa, and kept open an extensive communication along the shores of the Mediterranean, as well as with some parts of the interior[19]. The quadrangular form of these structures is the same as that used by the Romans in their stations and encampments; and the small number of troops which was allotted by the empire for the defence of Africa, made it peculiarly necessary that their garrisons should be well intrenched[20]. It has been calculated that a square of seven hundred yards was sufficient, according to the Roman method of encampment, for containing a body of twenty thousand men; and a square of one hundred feet would, at that rate, suffice for the accommodation of nine hundred and fifty. The habitable parts of the forts above mentioned very rarely exceeded a square of that size, and this portion of the structure, in by far the greater number of them, seldom amounted to sixty feet. As the nature of the country rendered it necessary to lay up stores of provision, a part of each fortress must have been set aside for that purpose, and it is probable that the greater number of the forts did not contain more than from fifty to two hundred men. The most perfect of those now remaining may perhaps have been constructed in the time of the emperor Justinian, when the victories of Belisarius and Solomon had restored the Roman authority in Africa: for it would then have been advisable to secure, by means of forts, the advantages which arms had obtained. The privations which were experienced by the army of Marcus Cato, in its march across the regions of the Syrtis, make it appear extremely probable that no stations or resting-places, had at that time been erected within their limits; and we may perhaps also infer that the fortresses of Euphrantas and Automala were not then available as places of accommodation. Should this have been the case, some of the forts and stations now existing, in various parts of the country in question, may be reasonably attributed to the well-founded policy of the emperors Augustus and Hadrian.