Popular reconstructions that show soldiers patrolling the top of Hadrian’s Wall have a powerful effect upon the viewer, but it is worth asking what evidence exists for such an interpretation of the structure of the curtain wall. Frontier walls are known in Tunisia and southern Germany that never had walkways on top of them.
Hadrian’s Wall is certainly broad enough to have accommodated a walkway with a parapet. Chamfered stones from an external string course have been identified as being a decorative feature associated with such walkways, as at the legionary fortress at Chester, and such stones are known in relative abundance from Hadrian’s Wall. The existence of steps at Milecastle 48 and possibly Peel Gap tower are important circumstantial evidence for the use of a walkway too.
If the Wall had a walkway, it will almost certainly have been crenelated.