Magnus Maximus (Latin: Flavius Magnus Maximus Augustus) (ca. 335 – August 28, 388), also known as Maximianus and Macsen Wledig in Welsh, was Western Roman Emperor from 383 to 388. As commander of Britain, he usurped the throne against Emperor Gratian in 383. However, through negotiation with Theodosius I the following year he was made emperor in Britannia and Gaul - while Gratian's brother Valentinian II retained Italy, Pannonia, Hispania, and Africa. Nevertheless Maximus' ambitions led him to invade Italy in 387, leading to his defeat by Theodosius at the Battle of the Save in 388. His death marked the end of real imperial activity in northern Gaul and Britain. After Maximus, no significant Roman emperor (ignoring shadowy and short-lived usurpers) ever went north of Lyons again.

http://en.wikipedia.org/wiki/Magnus_Maximus

Magnus Maximus alias Macsen Wledig (the Imperator), Emperor of the West, Abt 340 - 388

• m. Ceindrech ferch Reiden
  • Victor alias Gwidyr, Abt 354 - 388
  • Eugenius alias Owain Finddu (Black Lips), King of Mid-South Wales, Abt 355 -
• m. St. Helena of the Host, alias Elen Lwyddog, daughter of Octavius the Old alias Eudaf Hen, Abt 340
  • Antoninus Donatus alias Anwn Dynod, King of South-West Wales, Abt 357 -
  • Constantine alias Custennin Fawr (the Great), King of North-West Wales, Abt 360 -
  • Publicus alias St. Peblig of Llanbeblig, Abt 363 -
  • Gratianna, Abt 367 - , m. Tudwal ap Gwrfawr, King of Dumnonia, Abt 375 -
  • Severa, Abt 370 - , m. Vortigern Vorteneu (the Thin), King of Powys & All Britain, Abt 370 - Abt 459