Headed the first secession of the Welsh Marchers from the party of the opposition (1263), and was amongst the captives whom the Montfortians took at Lewes.
Hence the extraordinary slowness of their manoeuvres, not because the Austrian infantry were bad marchers, but because the preparation and circulation of orders was still far behind the French standard.
But he never desisted from his wars with the Marchers of South Wales, and in the early years of Henry III.
Thus, in the reign of Alexander, the fugitive serfs whom tyranny or idleness had driven into this wilderness (they were subsequently known as Kazaki, or Cossacks, a Tatar word meaning freebooters) were formed into companies (c. 1504) and placed at the disposal of the frontier starostas, or lord marchers, of Kaniev, Kamenets, Czerkask on the Don and other places.
A licence to enlist allies among the Welsh marchers, Dermot secured the aid of the Clares and Geraldines.