The Romans preferred to assault enemy walls by building earthen ramps ("agger") or simply scaling the walls, as in the early siege of the Samnite city of Silvium (306 BC). Soldiers working at the ramps were protected by shelters called "vineae", that were arranged to form a long corridor. Convex wicker shields were used to form a screen ("" or plute in English) to protect the front of the corridor during construction of the ramp. Another Roman siege engine sometimes used resembled the Greek ditch-filling tortoise, called a "musculus" ("muscle"). Battering rams were also widespread. The Roman Legions first used siege towers around 200 BC; in the first century BC, Julius Caesar accomplished a siege at Uxellodunum in Gaul using a ten-story siege tower. Romans were nearly always successful in besieging a city or fort, due to their persistence, the strength of their forces, their tactics, and their siege engines.