For protection against the attacks of the "free Dacians" (Dacians that lived outside Roman rule), Carpians and other neighbouring tribes, the Romans built forts and delimited the Roman held territory with a limes. Three great military roads were constructed, linking the chief towns of the province. Dacians were recruited into the Roman Army, and were employed in the construction and guarding of Hadrian's Wall in Britannia, or elsewhere in the Roman Empire. Several Cohors Primae Dacorum ("First cohort of Dacians") and Alae Dacorum fighting in the ranks of legions were stationed in Britannia at Deva (Chester), Vindolanda (on the Stanegate) and Banna (Birdoswald). In the third century, the attacks on Roman Dacia conducted by the Free Dacians and Goths intensified. Emperor Aurelian (270–275), confronted with the secession of Gaul and Hispania from the empire, the advance of the Sassanids in Asia and the devastations that the Carpians and the Goths had done to Moesia and Illyria, abandoned the province and withdrew the troops and administration, fixing the Roman frontier on the Danube. A new Dacia Aureliana was reorganised south of the Danube, with its capital at Serdica (modern Sofia). At the beginning of the next century, Romans had tried to retake control of the north of the Danube: in Constantine the Great's campaign from 332, 100,000 Goths were killed in battles on north of the Danube. For a very short time, near 328, there were plans regain administration of the north of the Danube; a stone bridge was erected between Sucidava and Oescus. After 334 AD, in Constantine the Great's campaign, 300,000 Sarmatians were evacuated from the north of the Danube, and the Roman limes were once again reestablished on Danube. During the Early Middle Ages, the Northern Balkan Peninsula became a conduit for invading tribes who targeted richer lands further west and south. Information about the military operations conducted in this period is very scarce. The territory of modern Romania was part of the Hun Empire, but after its disintegration different parts were under successive control of the Gepids, Avars, Slavs, Bulgars and Pechenegs. Most of these invaders did not permanently occupy the territory, as their organization was of typical nomadic confederacies.