How was Hadrian’s Wall built and defended?

Hadrian’s Wall was a sophisticated defensive system constructed primarily by soldiers from Britain’s three Roman legions to control frontier movement and deter barbarian incursions.1

Construction

The wall was built in layers, evolving through several design phases. The eastern sector featured a stone wall, while the western sector was initially built of turf before being gradually replaced with stone. The structure was fronted by a deep ditch to impede approach, except where natural crags provided sufficient defense. Behind the wall, the Romans constructed the vallum—a broad, flat-bottomed ditch flanked by continuous earth mounds—to serve as a rearward obstacle and define the military zone.12

Defense

The wall was not intended for fighting from the ramparts; instead, it functioned as a controlled barrier. The defense relied on:1
* Garrisoning: The wall was manned by second-line auxiliary troops trained to engage enemies in the open.1
* Infrastructure: The system included regularly spaced milecastles and towers for patrols, as well as 16 major forts for the fighting garrison, all connected by a rearward road.12
* Strategic Depth: Outposts were established to monitor territory beyond the wall, and the entire system was designed to manage low-intensity threats.12