It is believed that Saint Domangard or Donard founded a monastery in Maghera in the early christian period, c. 500 AD. He lived as a hermit on Slieve Donard, a nearby mountain that is named after him. There are no antiquities remaining from the early foundation but excavations in 1965 produced evidence of occupation around the tower during the Early Christian period. The medieval church situated behind the more modern church probably dates to the 12th century. It is much harder to date the round tower as there are no features such as windows or doors that normally help in dating round towers.
The tower, which is built from rough uncoursed granite field-stones similar to the tower at Castledermot, is believed to have fallen in the 18th century as a result of storm damage. All we see today is a 5.4 metre high stump with a large breech on the eastern side of the tower. This may represent the position of the doorway, suggesting a rather low entrance. The diameter of the tower at base level is 4.85 metres. The stones used in the building of the tower suggest a 10th century date but is not definite proof.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.