This work presents an incredible history of St. Cybi's Church, a medieval church around the Roman Caer Gybi in Holyhead, Anglesey, Wales. The original church was constructed at Holyhead in 540 AD by St Cybi, a cousin of St David. However, it was dismissed by Viking invaders in the 10th century and vandalized again in 1405 by Henry IV's invading force. Presently the church stands near the Roman fort in Holyhead and was built in the 13th century. This work includes the sermon preached on the reopening of St. Cybi's Church, after restoration in 1879, by Arthur Penrhyn Stanley.