The first polity that is believed to have included the whole of Bessarabia was the Dacian polity of Burebista in the 1st century BC. After his death, the polity was divided into smaller pieces, and the central parts were unified in the Dacian kingdom of Decebalus in the 1st century AD. This kingdom was defeated by the Roman Empire in 106. Southern Bessarabia was included in the empire even before that, in 57 AD, as part of the Roman province Moesia Inferior, but it was secured only when the Dacian Kingdom was defeated in 106. The Romans built defensive earthen walls in Southern Bessarabia (e.g. Lower Trajan Wall) to defend the Scythia Minor province against invasions. Except for the Black Sea shore in the south, Bessarabia remained outside direct Roman control; the myriad of tribes there are called by modern historians Free Dacians. The 2nd to the 5th centuries also saw the development of the Chernyakhov culture.