That broadening is not accidental. It marks where a weekly market was held, confirmed to the archbishops of Dublin in 1395, and the street's geometry has preserved that medieval function long after the market itself vanished. Swords today reads as an ordinary commuter town north of Dublin, but its street plan is essentially a fossil, the bones of a planned medieval borough still visible beneath the surface.

Archbishop Comyn established the borough in the late twelfth century, granting burgesses their burgages, the plots of land on which medieval town-dwellers held their properties, at an annual rent of one shilling per burgage. By 1326, an extent of the manor recorded 122 burgesses living and trading here. The town was laid out in a linear form along what medieval documents called High Street, the present Main Street, oriented towards the gates of the Archbishop's castle. A fourteenth-century deed mentions a lane called Le Camerothe running east to west, which may correspond to the modern Well Road or Seatown Road, though the identification is uncertain. Elizabeth I granted the settlement a new charter in 1578, making it a parliamentary borough, and this was confirmed again by James I in 1603. That same year of 1578 saw Swords counted among the walled towns of Dublin, though the precise circuit of those walls is only partially recoverable. The long property boundaries on the eastern side of Main Street likely reflect the defensive line, while a stream to the west and the ecclesiastical enclosure around the parish church may have formed further elements of the circuit.

By the nineteenth century, the physical fabric of the medieval town had largely gone. Writing in 1838, the historian D'Alton noted that several old inn buildings still carried their ancient painted signs, naming the Harp, the Anchor, the Black Bull, and the Royal Oak, and singled out the Anchor Inn as still drawing attention by its old appearance. None of these buildings survive. Visiting today, the most legible traces are spatial rather than structural: the widening of Main Street at its northern end, the long rear boundaries of properties on the eastern side, and the way the street still bends toward the site of the castle. Archbishop Alen's register contains numerous references to individual burgages and properties in the town, but none can be matched to any standing building or plot that exists today.