The earliest of these, dated to the tenth century, was not stone at all but an ovoid earthwork of earth and timber, thrown up along a natural ridge above the confluence of the Poddle and Liffey rivers. At Ross Road, the final phase of this embankment measured four metres high and five metres wide, topped by a timber palisade. It was functional rather than monumental, and parts of it served a secondary purpose as a flood barrier along Fishamble Street before anything more permanent was built.

Around 1015 AD the enclosed area expanded westward to take in High Street and Nicholas Street, and not long afterwards the earthen defences gave way to a Hiberno-Norse stone wall, the term referring to the hybrid Scandinavian-Irish culture that had developed in Dublin by that period. Built from massive locally quarried limestone blocks, this wall almost tripled the size of the defended area, running roughly from Parliament Street and Exchange Street Upper in the east across to Bridge Street in the west, and from Cook Street in the north down to Ross Road and Ship Street in the south. The Anglo-Normans arrived around 1170 and set about expanding and reinforcing what they found, raising funds for the work through murgage grants, a form of periodic toll levied specifically for wall-building and maintenance. Dublin's first charter dates from 1221. The curtain wall they developed was studded with mural towers, projecting structures that allowed defenders to cover the face of the wall, and punctuated by gates that a 1585 survey by Perrot described in some detail, noting that the southern gates were particularly formidable. At Dublin Castle, itself constructed in the angle of the existing walls, the Poddle was diverted to feed a rock-cut moat.

For anyone willing to look carefully, fragments of all this are still accessible at street level. The most substantial upstanding section of the medieval wall runs along Cook Street, where St. Audeon's Gate survives in heavily restored form. Sections are also visible at Lamb Alley and Ship Street Lower, and an 85-metre stretch of wall, standing around five metres high, connects Stanihurst's Tower on Ship Street Little to the boundary of Dublin Castle; the tower itself, named after James Stanihurst, recorder of Dublin, is an oddity in that it is circular on the exterior face and square on the interior. A long section of wall uncovered during excavations at Wood Quay is preserved inside the Civic Offices on the same site. Excavations at Dublin Castle in 1985 and 1986 exposed significant remains of several towers, including the Cork Tower at the north-west corner and the Powder Tower at the north-east, the latter sitting directly on bedrock above a rampart that had originally enclosed the Viking town.