The historic ruins of Monasterboice are of an early Christian settlement in County Louth in Ireland, north of Drogheda. Founded in the late 5th century by Saint Buite (who died around 521), it was an important religious centre until the establishment of nearby Mellifont Abbey by the Cistercians in 1142. The settlement was captured by invading Vikings in 968 AD, who were then comprehensively expelled by Donal, the Irish High King of Tara.

On the site, visitors can discover an old graveyard, two churches and a sundial but Monasterboice is most famous for its spectacular high crosses. Inside the ruins stands the impressive Muiredach's High Cross (5.5 metres high), regarded as the finest high cross in the whole of Ireland. It features biblical carvings of both the Old and New Testaments of the Bible and a copy is held in the Victoria and Albert Museum in London.

The crosses stand in the shadow of a magnificent round tower, about 35 metres high and divided into four or more stories inside, connected with ladders. The Monasterboice round tower was used as a watchtower and refuge for monks and valuables during times of Viking attack. In 1097, the interior is thought to have caught fire, an incident that destroyed many valuable manuscripts; the tower is currently closed to the public.

Visit Monasterboice to discover a lost world of Irish Christianity and explore the tranquil historic remains. Access to the site is across a minor road from the carpark. There are level, gravel-covered paths around the well-kept site, which has wheelchair access and toilet facilities. Guided tours of Monasterboice monastic site can be arranged on request.