The Pentland Firth (An Caol Arcach, meaning the Orcadian Strait) is a strait which separates the Orkney Islands from Caithness in the north of Scotland. Despite the name, it is not a firth.
The name is presumed to be a corruption of the Old Norse "Petlandsfjörð", meaning "the fjord of Pictland", and is completely unrelated to the Pentland Hills near Edinburgh.
Prior to the Norse occupation of Orkney the strait was known as the "Sea of Orcs" – a reference to the Pictish tribe who inhabited Orkney. Such was their marine prowess that there are also instances of this name referring to the sea lanes of the entire west coast of Scotland down to Kintyre. One version of the 9th-century Historia Brittonum states that "the Britons originally filled the whole island with their peoples from the English Channel to the Sea of Orcs".
On the Caithness (southern) side the Firth extends from Dunnet Head in the west to Duncansby Head in the east, while on the Or