Rathgar or Ráth Garbh meaning rough ringfort was used as a farm in the middle ages. The farm belonged to the Convent of St. Mary de Hogges but during the dissolution of manastries it was handed over to the Segrave family. The Segrave family built Rathgar Castle which was then handed over to John Cusack who was lord mayor of Dublin in 1608. The castle remained in the Cusack family for over a century, but unfortunatey over the years it began to decay and by the 18th century it was a ruin. No trace of the castle remains but it is thought to have stood on 44-49 Highfield road. The St. Mary de Hogges convent is now in College Green Dublin centre. The village of Rathgar started to develop in the 18th century. Rathgar Avenue is the oldest road, Highfield road was built in 1753. Zion church and Christ church were built in the 1860s and by that time Rathgar was a fairly big community.