Fathom Fathom A fathom is a unit of length in the imperial and the U.S. customary systems equal to , used especially for measuring the depth of water. There are two yards (6 feet) in an imperial fathom. Originally the span of a man's outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around . The name derives from the Old English word "fæðm", cognate
Fathom Castle (also referred to as 'the fort in the Forest') was abandoned and the Marmion family relocated to nearby fortified Carlingford (strongly defended by troops of King John's Castle.) The Marmions were prominent in the governance of Carlingford until 1655 when they were dispossessed for rebellion, losing their large holdings including a castle which was possibly the structure now referred to as 'The Mint'. Archaeological & Historical Society, 2000 Fathom Castle Fathom Castle, also known as Feedom Castle, was a castle in Fathom (sometimes 'Fidun') County Armagh near Newry, County Down, Northern Ireland. A stronghold of the O'Neill's, the castle was