The Orkney Islands lie off the northern tip of Scotland where the North Sea and the Atlantic Ocean meet. Comprising 67 islands, Orkney covers an area of approximately 376 square miles. Of the islands, less than one-third are inhabited, the islands having a total population of approximately 19,450 people. The majority of people live on Orkney's largest island, the land mass known as "the Mainland", with the greatest population concentrations being around the mainland towns of Kirkwall and Stromness. The islanders are often known as Orcadians; this comes from the Latin name of "Orcades", recorded by the Roman writer Diodorus Siculus around about the time of Julius Caesar's invasion of Britain.