1820 - 1840
Former Ulster Canal tunnel, built c.1830, running east-west under Old Cross Square. Now disused and largely obscured by vegetation. Segmental arch to west end, with squared, tooled stone voussoirs, squared stonework to vault, and squared rubble to parapet. Similar parapet to east end.
The Ulster Canal Tunnel, running under the square at the south-east side of Monaghan Town centre, is of considerable engineering importance as the longest canal tunnel in Ireland. Although barely registering on the streetscape and although the stretches of waterway leading to and from it have been compromised by road and building construction, the tunnel and canal are important reminders of the great era of canals in Ireland.