Hadrian's original plan was that his wall would be ten Roman feet (around 3m) thick, with a small fort and gateway (milecastle) every mile, and two look-out turrets between each pair of milecastles. Most of the troops would be based in large forts a mile behind the wall, along the Stanegate - the Roman road between the Tyne and Solway.

See a turret here and a milecastle here

The wall was built by the soldiers of the three legions based in Britain, the II Augusta, VI Victrix (Victorious) and XX Valeria Victrix (Valorous Victorious) - each building stretches of around 5-6 miles (8-10km) at a time. They began in the east, and gradually worked their way west. Each legion had its own distinctive style of building, which can be seen in the three different types of milecastle, varying in plan and in the form of the gateway. While the eastern three-fifths of the wall was built in stone, the western two-fifths was originally made from turf, later replaced with stone. North of the wall, apart from in places where it ran along high crags, they dug a defensive ditch.

When construction was well advanced, changes were made to the plan. A dozen large garrison forts were placed along the line of the wall, which was also narrowed by two feet, to speed up construction. This suggests that the soldiers had met opposition from the local tribes, and needed to defend themselves while they continued their building work. Another late addition was a wide road running immediately behind the wall, defended on its south side by the "vallum", a ditch flanked by earth embankments.

See the vallum running alongside the Newcastle to Carlisle road here

Hadrian's Wall was never thought of as an absolute barrier, but as a way of supervising the movement of local tribes, like a modern border checkpoint. The Romans also thought of lands immediately north of the wall as under their control, for they built seven outpost forts here.