Ardglass has been a fishing port for more than two thousand years. The natural inlet here, accessible at every state of the tide, gave the Anglo-Norman traders of the late Middle Ages a working harbour while better-placed rivals dried out twice a day. By the 1400s the grain trade had made Ardglass rich enough that its merchants ringed their warehouses with stone towers, the most extensive network of medieval warehouses to survive in Ireland. Then the focus of Ulster trade shifted, and Ardglass slept for three hundred years. No real harbour works went up until after 1812, when William Ogilvie bought the estate and rebuilt the pier. Today the port is quieter than its medieval peak, but the boats still come in. Up to five million pounds passes through the herring, prawn and whitefish trade each year.

On 27 November 1838, a great storm tore the new lighthouse off the end of the Ardglass pier and dropped it into the sea. The harbour master who inherited that broken pier in 1845 was Captain Bernard Hughes, a man who would spend the next thirteen years trying to make Ardglass into something it would never quite become. When Brunel's SS Great Britain ran aground in Dundrum Bay in 1846, Hughes helped with the salvage. The experience convinced him that the northeast Irish coast needed a Harbour of Refuge, and Ardglass should be it. He wrote to the Admiralty. He wrote to the press. He invented and patented a new method of building sea walls without mortar, so that the stones could shift under wave action without breaking. The Admiralty never gave him his harbour. But the Hughes family went on to produce two generals, a vice-commodore of Elder Dempster, the staff captain of the RMS Mauretania, and an Air Marshal who commanded RAF Transport Command. Not bad, for a harbour master who never quite won his argument.

Francis Joseph Bigger, the Belfast solicitor and Irish nationalist, bought Jordan's Castle in 1911 and rechristened it Castle Sean. He restored its battered tower as a meeting place for the Celtic Revival, hosting figures like the historian Alice Stopford Green among its medieval stones, and eventually bequeathed it to the state. A short walk away, on a hill above the village, sits Isabella's Tower, a folly built around 1830 by Aubrey de Vere Beauclerc as a gazebo where his invalid daughter could sit and watch the sea. Up the coast at Ardtole, the roofless fifteenth-century church still stands on its hilltop, the Isle of Man on a clear day visible across the Irish Sea. None of these were grand aristocratic projects. Tower houses, in the Irish countryside, were the architecture of lesser lords and gentry, of merchants who could afford stone but not splendour. Ardglass is the shape that money took here, before the trade moved on.

The marina at Ardglass goes by an older name too, Phennick Cove, and on a quiet summer evening with the prawn boats tied up at the South Pier it is easy to forget the harbour was ever anything else. Eight archaeological sites lie within the village, two more nearby. The 1996 conservation area was drawn around the early-nineteenth-century street pattern that William Ogilvie laid out, but the medieval bones show through everywhere, in the angle of a wall, in the squared stones of a doorway. The disused railway station, where the Belfast and County Down line ended its run from 1892 until the closures of 1950, is one more layer over the older ones. Ardglass keeps adding pages without throwing the old ones away.