One of the main attractions at the local museum in Newry, a bustling market town some 40 miles south of Belfast, is an old wooden sign.
Painted on a chalky white background, its tall red letters proclaim in Irish, then in English: “Custaim: Stad, Customs: Stop.”
For decades, this sign stood on the road between Newry, in Northern Ireland, and Dundalk, in the Republic of Ireland, demarking the twisting, 500-kilometer border between the two countries. The sign was taken down when Ireland and the United Kingdom joined the European Union’s single market in 1993. By the time the Good Friday Agreement was signed in Belfast in 1998, it was easy to forget the border even existed.