[1] It adjoins Colwyn Bay and is named after the Welsh kingdom of Rhos established there in late Roman Britain as a sub-kingdom of Gwynedd.

Bryn Euryn is a hill overlooking Rhos-on-Sea on which there are the remains of a hillfort called Dinerth, the 'fort of the bear', and a limestone quarry.

[2] Ednyfed Fychan, 13th century seneschal to Llywelyn the Great and ancestor to the House of Tudor was granted the land and built a castle on the hill, of which all traces have disappeared, and a manor, Llys Euryn of which the ruins of its 15th-century reconstruction can be seen today.

[6] In 1186 Llywelyn the Great permitted the establishment of the Cistercian Aberconwy Abbey, and the monks built a fishing weir on the sea shore below Bryn Euryn.

[2] The weir continued to provide a prosperous livelihood through to the early 20th century: during a single night in 1850, 35,000 herring were caught, and 10 tons of mackerel were removed in one tide as late as 1907.

[9] Because such weirs decimated inshore fish stocks, Parliament banned them in 1861 unless it could be shown they pre-dated the Magna Carta, which the then owners, the Parry Evans family, were able to prove.

Saint Trillo, the son of Ithel Hael from Llydaw (Brittany) also founded a church at Llandrillo in Denbighshire.