Millmount Castle in Drogheda formed part of the town's defenses during the 1649 Siege of Drogheda by Oliver Cromwell, where the English defenders were massacred when they surrendered. The complex was later fortified after the 1798 rebellion and 1800 Act of Union. It suffered damage during the Irish Civil War when anti-treaty forces occupied it and it was shelled by the Irish Free State army in 1922 using the same artillery piece that shelled Dublin. Millmount Castle is now open to the public as a museum providing tours and boosting the local economy.