The cities of Scotland and Ireland were treated separately. Scottish towns irregularly applied the description to themselves, but were formally organised as royal burghs; the special rights of these were preserved by Article XXI of the Treaty of Union which established the single state of Great Britain in 1707. Edinburgh and Glasgow were confirmed as cities "by ancient usage" in the 18th century, as was Aberdeen, and this was later reconfirmed in the Act enlarging the burgh in 1891. Dundee was granted letters patent in 1889 and Elgin and Perth were recognised as cities by the Home Office in 1972, before the privilege was removed by the Scottish Local Government Act of 1973.