Conversation so far:
When did the reign of Gwynedd begin in Wales?
Maelgwn Gwynedd was king of Gwynedd during the early 6th century.
Who were the Britons fighting after the Romans left Britain?
The Britons were fighting invading Gaelic tribes from Ireland.
How did Britons' conquest of Wales over the Irish Gaelic tribes go?
Maelgwn Gwynedd's father Cadwallon Long-Hand completed the process by destroying the last Irish settlements on Anglesey.
Who started Britons' conquest of Wales over the Irish Gaelic tribes?
The kingdom of Gwynedd began with the reconquest of the Welsh coast by northern Britons under the command of Maelgwn Gwynedd's great-grandfather Cunedda Wledig.
Where did the name Gwynedd come from?
Gwynedd is believed to be an early borrowing from Irish, either cognate with the Old Irish ethnic name Féni, Irish People, or war band.
When did Maelgwn Gwynedd's reign end?
Maelgwn Gwynedd died in 547 AD.
What was at Llanrhos in regards to Maelgwn Gwynedd?
Tradition also holds that Maelgwn Gwynedd died at Llanrhos, and was buried there.
What was nearby Llanrhos?
Deganwy, in the Creuddyn peninsula of Rhos.
What was at Deganwy in regards to Maelgwn Gwynedd?
By tradition, Maelgwn Gwynedd's llys was located at Deganwy, in the Creuddyn peninsula of Rhos.

Question: What was his Ilys?
Self-contained rewrite: What was Maelgwn Gwynedd's Ilys?