York City Walls

The original walls were built around 71 AD, when the Romans erected a fort (castra) occupying about 50 acres or 21.5 hectares near the banks of the River Ouse. The rectangle of walls was built as part of the fort's defences. The foundations and the line of about half of these Roman walls form part of the existing walls. Some call the existing city walls "Roman walls" which is a misnomer as very little of the extant stonework is of Roman origin, and the course of the wall has been substantially altered since Roman times. The majority of the remaining walls, which encircle the whole of the medieval city, date from the 13th – 14th century.

Most of the Roman walls are underground, and are overlaid with centuries of modification including Danish and Norman ramparts. Example cross-section of the walls can be viewed at british-history.ac.uk/rchme/york/vol2/pp108-138.With 6 Bars (gatehouses), 8 posterns and 39 towers (not all have survived), you can't come to York and not walk some of the walls, the most scenic parts are the North Corner around the Minster on the north side of the city centre.
Opening times and other notices here: york.gov.uk/york-city-centre/city-walls/3
Maps and descriptions of wall walks here: yorkwalls.org.uk/?page_id=3690