The Benediction of Saint Patrick
According to folklore, Saint Patrick lit the first paschal fire on the Hill of Slane in direct defiance of the druids and the pagan Kings of Tara, from which the fire could be seen. His group was arrested, but he talked so eloquently to King Laoghaire that he gained pardon and freedom to preach across the land. Pivotal in the history of Ireland.
I spotted the rainbow when we had come down the hill after our visit to the viewpoint and ruins on top, so I had to run back up the hill to the graveyard to get this photo. I managed to only get this one before the rainbow disappeared.
It's from my pre-digital camera days, so has lost some quality in the scan. The colour/B&W effect is the "focal B&W" effect in Picasa - I'm not normally one for this kind of thing but felt it fitted this image. :)