Piers de Ros (a name that seems to have been taken from Ros, Holderness, East Riding Yorks); steward to Count d'Aumale (feudal Lord of Holderness); married Adeline, 3rd and youngest sister and coheir of Walter Espec, feudal Lord of Helmsley, Yorks, and Wark, Northumberland. [Burke's Peerage]
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"That Peter, the ancestor of this great and noble family," says Dugdale, "did originally assume his surname in the time of Henry I from that lordship in Holderness called Ros, where he then had his residence, needeth not to be doubted." This Peter de Ros, or Roos, a feudal baron, m. Adeline, one of the sisters and co-heirs of the famous Walter Espec, Lord of the manor of Helmesley, called sometimes Helmeslac, but oftener Hamlake, in the north riding of Yorkshire, and was s. at his decease by his son, Robert de Ros. [Sir Bernard Burke, Dormant, Abeyant, Forfeited and Extinct Peerages, Burke's Peerage, London, 1883, p. 458, Ros, or Roos, Barons Ros]