Now part of the diocese of Kildare and Leighlin, several Early Christian settlements are still in evidence today around the county. St Mullin's monastery is believed to have been established around the 7th century, the ruins of which are still in evidence today. Old Leighlin was the site of one of the largest monastic settlements in Ireland and the location for a church synod in 630 AD which determined the date of Easter. St Comhgall built a monastery in the Carlow area in the 6th century, an old church building and burial ground survive today at Castle Hill known as Mary's Abbey. Carlow was an Irish stronghold for agriculture in the early 1800s which earned the county the nickname of the scallion eaters. Famine later wiped out half of the population.