Astorga was Asturica Augusta, founded in the late first century BCE as a base for Augustus's wars against the Cantabrian and Asturian tribes, and became the administrative capital of Roman gold mining in northwest Iberia. The ramparts that survive — best seen on the western side of town between the cathedral and the Jardín de la Sinagoga — were built in the late third and early fourth centuries, when the original civilian town was fortified against unrest. They form an almost complete polygon enclosing the medieval centre.
The walls are walkable on top in places. Combine with the Roman Museum and the open-air Ergástula archaeological site for a sense of the Roman city beneath the present one.