The Castlestrange stone is located in the grounds of "Castlestrange House" near Athleague in County Roscommon. It is a granite boulder decorated with flowing spirals in the La Tène style, dating from the Iron Age period between 500 BC and 100 AD.
It is believed that there was a strong Continental influence in Ireland at the time, which the carver was imitating.
Only three other stones of this type have been found in Ireland, of which the Turoe stone in County Galway is the best known. The use of the stones is not known but it is assumed they served some religious or ritual purpose.
The stone is a protected National Monument.