If you stand in front of Kilmainham Courthouse and look east you will see an impressive mock-Tudor gatehouse guarding the western entrance to the Royal Hospital Kilmainham. But it didn't always guard the western entrance. It was originally built as Richmond tower (or the Watling St Gatehouse) at the end of the south quays, at the foot of Watling St, and at the site of the then Barrack Bridge (now Rory O'More Bridge). The bridge and gatehouse connected the traffic from the city and military buildings north of the river, such as the Royal Barracks (now Collins Barracks), to the Military Road leading to the Royal Hospital, and to Richmond Barracks.
The tower was built in 1812 by renowned architect Francis Johnston (who also gave us the original GPO, and the Chapel & Tower in Dublin Castle) and opened that same year by Charles Lennox 4th Duke of Richmond and then Lord Lieutenant of Ireland. It bears his coat of arms on the outside of the gate arch - perhaps also incorporating his wife's. Charles was a keen cricketer and a founder member of Marlybone Cricket Club. His stint as Lord Lieutenant of Ireland came to an uneventful end in 1813. His wife, Lady Charlotte Lennox (nee. Gordon) hosted the eponymous "Duchess of Richmond's Ball" in Brussels on 15th June 1815 - the night before the Battle of Quatre Bras at Waterloo. He went on to become Lord Lieutenant of Canada in 1818 but was bitten by a rabid fox and died in 1819.
When the Great Southern and Western Railroad (GS&WR) opened their impressive station at the King's Bridge (now Heuston Station) in 1846 the gatehouse on the quays became an impediment to growing traffic along the quays to the station. So the GS&WR moved it, stone by stone and at their own cost, to its new location, a mile as the crow flies. The move was almost perfect - except for a few blocks that were damaged in transit. These were repaired with iron ties which have since rusted leaving distinctive brown rust marks on the face of the tower. The tower also gained the coat of arms of the Royal Hospital - granted in 1847 - which are on the inside of the gate arch.
Conditions in the tower for guards were rudimentary as can be seen from the crude outside urinals situated to the right of the tower and manufactured by Shanks of Barr Head just outside Glasgow.