Croagh Patrick, previously known as Cruachan Aigle, has been a sacred mountain since prehistory. It is on this mountain, according to folk tradition, that Patrick gathered the snakes before banishing them from Ireland. Here, the saint fasted for 40 days and 40 nights with giant birds circling above him. His first major escapade in Ireland was the lighting of the sacred flame of the Paschal Fire atop the Hill of Slane, in direct contravention of the Irish law which forbade the ignition of any Easter fire before the sacred fire had first been tindered by the King on the Hill of Tara. Remarkably, Croagh Patrick and Slane are part of a huge alignment system, stretching from the east coast of Ireland to the west, across more than 135 miles of landscape. The alignment starts at Millmount, not far from where Patrick landed on the Boyne Estuary, and continues through Slane and Kells towards the Cruachan Ai complex in Roscommon, the home of the Connaught kings and Queen Medb's stronghold. The alignment also follows the Tóchar Padraig, Patrick's causeway, a pilgrim route which follows a path across 20 miles of countryside from Ballintubber Abbey through Aghagower to Croagh Patrick. On the last Sunday of every July, pilgims flock to the holy mountain to climb to the summit.

Highest points by county in Ireland.  Antrim Trostan 550 / Armagh Slieve Gullion 573 / Carlow Mount Leinster 795 / Cavan Cuilcagh 665 / Clare Moylussa 532 / Cork Knockboy 706 / Donegal Errigal 751 / Down Slieve Donard 850 / Dublin Kippure 757 / Fermanagh Cuilcagh 665  / Galway Binn Bhn 729 /  Kerry Carrauntoohil 1039 /  Kildare Cupidstown Hill 379 /  Kilkenny Brandon Hill 515 /  Laois Arderin 527 /  Leitrim Truskmore 647 /  Limerick Galtymore 919 /  Londonderry (Derry) Sawel 678 /  Longford Corn Hill 278 /  Louth Slieve Foye 589 /  Mayo Mweelrea 814 /  Meath Carnbane East 279 /  Monaghan Slieve Beagh East 366 /  Offaly Arderin 527 / Roscommon Corrie Mountain 422 /  Sligo Truskmore 647 /  Tipperary Galtymore 919  Tyrone Sawel 678 /  Waterford Knockmealdown 794 /  Westmeath Mullaghmeen 258  / Wexford Mount Leinster 795  Wicklow Lugnaquilla  925 .