A 1682 survey estimated that the summit of Snowdon was at a height of ; in 1773, Thomas Pennant quoted a later estimate of above sea level at Caernarfon. It was long believed to be the tallest mountain on the island of Great Britain until measurements taken in the eighteenth century confirmed that Ben Nevis, along with several other Scottish peaks, were taller. Recent surveys give the height of the summit as , making Snowdon the highest mountain in Wales, and the highest point in the British Isles outside Scotland.