This is a list of P600 mountains in Britain and Ireland by height. A P600 is defined as a mountain with a topographic prominence above , regardless of elevation or any other merits (e.g. topographic isolation); this is a similar approach to that of the Marilyn, Simms, HuMP and TuMP British Isle mountain and hill classifications. By definition, P600s have a height above , the requirement to be called a "mountain" in the British Isles. The "P" terminology is an international classification, along with P1500 Ultras. P600 and "Majors" are used interchangeably. , there were 120 P600s in the British Isles: 81 in Scotland, 25 in Ireland, 8 in Wales, 4 in England, 1 in Northern Ireland, and 1 in the Isle of Man. The 120 P600s contained 54 of the 282 Scottish Munros, and 10 of the 34 Non-Scottish Munros (or Furths), all of which have prominences above , and are sometimes called the "Super-Majors". The list also contained the highest mountains in Scotland, Wales, Ireland, and England. On 9 November 2019, Norfolk climber Liam Chase became the first person to complete all 120 P600s in a single calendar year, starting with Cross Fell on 1 January, and ending with Pen y Fan. Chase was also only the seventh person recorded to have climbed all P600s over any time period. P600 mountains by height British Isles mountain cartographer, Alan Dawson, developer of the Marilyns designation, labelled "Majors" as having a prominence of over , but no other criteria. Dawson's prominence threshold was the normal height threshold for a British Isles mountain, and 111 mountains met his definition. In 2004, Dawson's prominence was converted into a metric threshold of by Rob Woodall & Jonathan de Ferranti, and labelled the "P600s", a term used by the UIAA for major mountains; the P600s expanded to 119 mountains. The current list has 120 mountains, although there is dispute as to whether Moel Siabod's prominence is above 600 metres (2,000 ft), or is in fact just below the threshold at 599.9 metres. This list below was downloaded from the Database of British and Irish Hills ("DoBIH") in October 2018. Note that topographical prominence, unlike topographical elevation, is far more complex to measure and requires a survey of the entire contours of a peak, rather than a single point of height. These tables are therefore subject to being revised over time, and should not be