Castlestrange stone, Iron Age stone monument near Athleague, Ireland.

The Castlestrange stone is a granite boulder in the grounds of Castlestrange House near Athleague, County Roscommon, carved with flowing La Tène-style spirals. It is one of only four such stones found in Ireland, alongside the Turoe, Killycluggin and Derrykeighan stones.

The Castlestrange stone is a granite boulder carved with flowing La Tène-style spirals, made in the Iron Age; sources date it between 300 BC and 100 AD, with one Russian account giving 500 BC to 100 AD. Its carver is thought to have imitated continental La Tène art, which was then influencing Ireland. It is one of only four such stones found in Ireland, alongside the Turoe, Killycluggin and Derrykeighan stones, and is a protected National Monument.

The flowing La Tène spirals are thought to imitate continental Celtic art that reached Ireland in the Iron Age. The stone's purpose is unknown; it is assumed to have served a religious or ritual role. It now stands as a protected National Monument in the grounds of Castlestrange House.

The stone sits on the grounds of Castlestrange House and is open to visitors throughout the year at no cost. Since it stands on private property, it is wise to check local access arrangements before planning your visit.

The Castlestrange stone is one of only four La Tène-decorated stones found in Ireland, alongside the Turoe Stone in County Galway, the Killycluggin Stone in County Cavan and the Derrykeighan Stone in County Antrim. On a map the four lie on roughly the same line across the island, though the sources record no explanation for this.