Gemellae
About
Gemellae was the best-studied strongpoint of the Fossatum Africae, its ditch and rampart mapped in detail by aerial photography on the edge of the Sahara. It was established around 126 CE under Hadrian, roughly a decade after Trajan's death, so it falls outside this snapshot even though it anchors the frontier system the Trajanic sections fed into.
What happened here
Five hundred men, sometimes a thousand, recruited from a province rather than from citizens, and often stationed a long way from where they were raised. Cavalry units get a bigger fort and far more stabling; the smell tells you which kind you are in before the plan does. The layout copies a legionary fortress at a quarter of the size — headquarters, commander's house, granaries, barracks, a bath house usually built outside the walls because of the fire risk. Duties are patrolling, escorting, customs, and policing rather than pitched battle. After twenty-five years a man is discharged with citizenship for himself and his children, recorded on a bronze diploma he keeps for life. A village grows outside the gate within a decade.
Sources
Roman Maps shows the empire frozen at 11 August 117 CE, the day Trajan died — its moment of greatest territorial extent. Explore the full map →