210 of them, from tombs older than the pyramids to the bell towers of the monasteries, each placed on the map by its real coordinates. Six kinds, six pages, and one honest rule: where nobody knows what a thing was for, the page says so.
Pins are Wikipedia's coordinates for each article; towers without a documented location are listed on their page but not pinned.
The megalithic tombs. The court tombs of the north were being built from about 3900 BC and the great passage tombs of the Boyne valley around 3200 BC — older than Stonehenge's sarsens and the pyramids of Giza. Everything else on this map, from the round towers to the high crosses, is Christian and at least three thousand years younger.
67 survive in some form on Barrow's survey, from complete towers of thirty metres to stumps of a few. Two more stand in Scotland and one on the Isle of Man.
On this map Cork, with 21, then Kerry with 19. That reflects what has a documented article, not a survey of the ground — the true numbers run into the thousands for tombs and holy wells alone.
They have their own map: 354 castles, county by county, at /castles/. This page is for what came before the castles and what stood beside the churches.
The castles, county by county · The saints whose monasteries these were · Hidden Ireland on the atlas