The 5th-century historian
Zosimus strongly criticised the establishment of the large
comitatus, accusing Constantine of wrecking his predecessor Diocletian's work of strengthening the border defences: "By the foresight of Diocletian, the frontiers of the Roman empire were everywhere studded with cities and forts and towers... and the whole army was stationed along them, so it was impossible for the barbarians to break through... But Constantine ruined this defensive system by withdrawing the majority of the troops from the frontiers and stationing them in cities which did not require protection."
[78] Zosimus' critique is probably excessive, both because the
comitatus already existed in Diocletian's time and because some new regiments were raised by Constantine for his expanded
comitatus, as well as incorporating existing units.
[79] Nevertheless, the majority of his
comitatus was drawn from existing frontier units.
[66]This drawdown of large numbers of the best units inevitably increased the risk of successful large-scale barbarian breaches of the frontier defences.