In the south of Mauritania Tingitana the frontier in the third century lay just north of Casablanca near Sala and stretched to Volubilis. Septimius Severus expanded the "Limes Tripolitanus" dramatically, even briefly holding a military presence in the Garamantian capital Garama in 203 AD. Much of the initial campaigning success was achieved by Quintus Anicius Faustus, the legate of Legio III Augusta. Following his African conquests, the Roman Empire may have reached its greatest extent during the reign of Septimius Severus, under whom the empire encompassed an area of 2 million square miles ( million square kilometers). Fossatum Africae ("African ditch") is a linear defensive structure ("limes") that extended over 750 km or more in northern Africa constructed during the Roman Empire to defend and control the southern borders of the Empire in the Roman province of Africa. It is considered to have many similarities of construction to Hadrian's Wall at the northern border of the Empire in Britain. Generally the Fossatum consists of a ditch and earth embankments on either side using the material from the ditch. Sometimes the embankments are supplemented by dry stone walls on one or both sides; rarely, there are stone walls without a ditch. The width of the Fossatum is generally 3–6 m but in exceptional cases may be as much as 20 m. Wherever possible, it or its highest wall is constructed on the counterscarp. Excavations near Gemellae showed the depth there to be 2–3 m, with a width of 1 m at the bottom widening to 2–3 m at the top. The Fossatum is accompanied by many small watchtowers and numerous forts, often built within sight of one another. Roman writers and subsequent authors who depended on them presented the "limes" as a sort of sacred border beyond which human beings did not transgress, and if they did, it was evidence that they had passed the bounds of reason and civilization. To cross the border was the mark of a savage. They wrote of the Alemanni failing to respect the "limes" as if they had passed the final limitation of character and had committed themselves to perdition. The Alemanni, on the other hand, never regarded the border as legitimate in the first place. They viewed the Romans as foreigners, who changed native place names and intruded on native homes and families. They were only to be tolerated because they were willing to pay cash for the privilege and also offered the blandishments of civilized life.