The flag of Welsh rebel leader Owain Glyndwr will fly above the battlements of Cardiff Castle all week from Monday.
Owain Glyndwr's standard will be flown in Cardiff Bay again
It is believed to be the first time the standard bearing his coat of arms has been hoisted above the castle for more than 600 years.
Cardiff Council agreed the yellow and red "Four Lions Rampant" flag could be flown to celebrate Owain Glyndwr Day.
Glyndwr established a Welsh parliament and was proclaimed Prince of Wales on 16 September 1400.
The decision to mark Glyndwr Day in this way follows a number of requests from members of the public.
The flag of Glyndwr will fly over the east battlements of Cardiff Castle.
Cardiff council executive member for sport, leisure and culture Nigel Howells said he was "delighted" that the flag would be flying from the castle.
"Glyndwr was one of the key figures in Welsh heritage and it's fitting that we remember him this way," he said.
Glyndwr capitalised on the anti-English feeling in Wales in the early 15th century.
Backed by French military aid, Glyndwr took Carmarthen and Cardiff from the English in 1403 and Harlech and Aberystwyth in 1404.
But the tide turned against the Welsh as England's superior resources and weaponry were turned on them under the leadership of the future Henry V.
By 1409, the revolt was broken and the many towns and castles Glyndwr had taken were lost. He was forced to turn to guerrilla warfare until his death in 1416.