A Marilyn is a hill of any height with a drop of 150 metres or more on all sides. In other words, a relatively high hill. The British Marilyns are all listed in a book called The Relative Hills of Britain (RHB) by Alan Dawson, published by Cicerone Press in April 1992. Details of subsequent changes have been published in a series of update sheets.
The total number of Marilyns is now 1555, following the demotion of Cruim Leacainn (4A), Troweir Hill (27B) and Swyre Head (41), and the promotion of Creag an Amalaidh (16D). Details up to April 2014 are available in the latest update to RHB.
On 13 October 2014, Rob Woodall and Eddie Dealtry climbed Stac an Armin and then Stac Lee, and so became the first people to finish the Marilyns.