Bold Gryffindor, from wild moor,
Fair Ravenclaw, from glen,
Sweet Hufflepuff, from valley broad,
Shrewd Slytherin, from fen.
-- The Sorting Hat (GF12)
A fen is an alkaline wetland, in Britain found mostly near the eastern shore of England, in and near Norfolk. According to one of the Sorting Hat’s songs, Salazar Slytherin came from fen, suggesting that he was most likely from the eastern part of England (GF12).