The town’s name comes from the Irish “Beal Atha Seanaidh”, meaning “the mouth of the ford of the hill-slope”, and this ford has long been the key to controlling movement between Connacht and Tirconnell. The strategic importance of this spot is underlined by a remarkable discovery from 1916, when a fisherman’s net brought up a bronze sword hilt dating to the 1st century BC, likely imported directly from Gaul, suggesting the harbour here has been drawing traders since prehistoric times.

The struggle for control of Ballyshannon reads like a military history of Ulster itself. The Anglo-Normans tried and failed to establish themselves here in the 13th century, with a major battle fought at the ford in 1247. O’Donnell built a castle here in 1423, recognising that whoever held Ballyshannon controlled access to Tirconnell. During the Nine Years War, it became one of the most hotly contested sites in Ireland; Sir Conyers Clifford met defeat here in 1597, and it took Sir Henry Dowcra with artillery support to finally capture the castle in 1602. After the war’s conclusion, the English government retained the castle along with 1,000 acres for developing a planned town, which Sir Henry Foliott established as a borough in 1613. Despite its strategic importance, the settler population remained modest; a census around 1659 recorded just 63 English and Scots alongside 71 Irish inhabitants.

The town’s layout tells its own story of gradual development from a military outpost to a market town. The original street plan was essentially linear, centred on Main Street with Castle Street and Market Street branching off at angles. Archaeological investigations throughout the town have revealed surprisingly little from its turbulent past; test trenches dug at various sites along Main Street, Bishop Street, and the Mall have mostly turned up modern fill and 19th-century material rather than medieval remains. The original marketplace likely stood at the junction where Market, Main, and Castle Streets converged, whilst areas like the Mall and College Street represent later additions to the urban fabric. South of the river, East Port and West Port may preserve the locations of early suburbs that grew outside the fortified core of the plantation town.