The "limes" in Britain ("Limes Britannicus") is on the territory of the present-day United Kingdom in England, Scotland and Wales. From the 1st to the 2nd century, the Gask Ridge and the Stanegate, with their chains of Roman camps and watchtowers, marked the northern boundary of Britannia. Later the isthmuses in the north between the Firth of Forth and Firth of Clyde were guarded by the defences of the Antonine Wall and the line between the mouth of the Tyne and Solway Firth by Hadrian's Wall. The perimeter defence of Hadrian's Wall was achieved through the construction of camps ("castella") on the lowlands, which were built along the most important roads in the north. Security and monitoring on the coasts in the west and southeast was achieved by camps and by chains of watchtowers or signal towers, both along the coastline and along main roads in the interior.