Although Londinium remained important for the rest of the Roman period, no further expansion resulted. Londinium supported a smaller but stable settlement population as archaeologists have found that much of the city after this date was covered in dark earth—the by-product of urban household waste, manure, ceramic tile, and non-farm debris of settlement occupation, which accumulated relatively undisturbed for centuries. Sometime between 190 and 225, the Romans built a defensive wall around the landward side of the city. Along with Hadrian's Wall and the road network, this wall was one of the largest construction projects carried out in Roman Britain. The London Wall survived for another 1,600 years and broadly defined the perimeter of the old City of London.