Frieda, Sigurd Towrie has several pages on the Brough: http://www.orkneyjar.com/history/broughofbirsay/index.html I don't think anyone normally uses a boat to visit it. After all, it's easy enough for an able-bodied person to walk across the causeway at some point during the day, so why pay a boatman? In any case I think that, because of the cliffs around the island, there's really only one point at which one could get onto it, and that's more or less at the end of the causeway. I suspect that even at high tide there wouldn't be a great depth of water there and that it would be very easy to damage a boat on the rocks. You mention Picts, Christians and Vikings. There is certainly archaeological evidence of the Pictish occupation of the island, and a lot more of the Viking presence. I'm not sure if the Picts were Christian (though they probably were, as far as I can gather) but the Vikings most certainly were. Sigurd Towrie says, "The earliest settlement on the Brough is thought to date from the fifth century AD, perhaps Christian missionaries." I don't know what evidence there is for that. I can't see any mention of it in Anna Ritchie's "Historic Scotland" booklet on the Brough, but the copy I have dates from 1988 and there may have been more recent archaeological evidence of a pre-Pictish settlement. I'm not aware of any caves on the Brough, or of pirates using it. Neither was there any building on it after Viking times, apart from the lighthouse (built in 1925). Norman Tulloch