The wall did not stop at the Solway. Along the Cumbrian coast, south of Bowness, the Romans built a chain of small forts, milecastles and watchtowers to guard against raiders arriving by sea from across the Irish Sea, and Brownrigg milecastle 22 is one of them. It stands on a low ridge above the shore near Maryport, with views across the Solway Firth to the hills of Scotland, a line of blue on a clear day. Little remains but a platform and some stonework, but the situation says everything.
Maryport itself was the site of a Roman fort called Alauna, on a headland above the harbour, and a good museum in the town displays the altars found there, dedicated to Jupiter and to the emperor. The fort is thought to have been an important supply base for the coastal defences. The town grew up later as a coal and iron port, laid out in a neat Georgian grid in the eighteenth century by the Senhouse family, who owned the land. The harbour is still lively, and the quay is a good place to watch the tide and the gulls.
The coast road here is a quiet, wide-skied ride. It runs along the edge of the Solway Plain, a low, green country of farms, dunes and marshes, with large flocks of wading birds in winter and a broad sky that seems to hold the light for longer than elsewhere. The road is mostly smooth and open, with long bends and few hills, and traffic is light except on summer weekends. The wind off the sea can be fierce, so keep your speed moderate, and watch for sand and mud on the road near the shore, particularly after high tides.
In the east, the Lake District fells stand like a blue wall, and the contrast between the flat coast and the mountains behind is striking. The Roman frontier here was a sea frontier, and the land itself tells the story.
Maryport has nearly ten thousand people, so fuel, shops and fish and chips are easy. Check tide times before walking on the shore, and bring a windproof jacket.