HAD Algeria and Morocco honoured their agreement back in 1989 to form an economic union, along with Tunisia, Libya and Mauritania, they would be among the Middle East’s largest economies. Their poor border regions would be booming crossroads. Over the decade to 2015, reckons the World Bank, their two economies would each have almost have doubled in size.

Instead, Algeria grew only by 33% and Morocco by 37%, as both governments instead reinforced their barricades. Their north-west corner of Africa remains “the most separated region on the continent”, says Adel Hamaizia, an Algerian economist. While sub-Saharan countries agree common currencies and trade zones, Algeria digs deeper ditches. Morocco revamps its berms and renews its razor wire. Concrete walls rise on both sides. Frustrated families shout greetings across the divide. Tantalisingly, both have built hundreds of kilometres of east-west highways which stop short of their common border.

Islamic empires once spanned the Maghreb, the land of the setting sun, as Arabs term north-western Africa. Both countries share a common history, cuisine, architecture, strand of Islam and an Arabic dialect mashed with Berber and French. But in 1957 colonial French generals erected an electrified barrier, the Morice Line, along the border to keep out arms-traffickers and guerrillas based in newly independent Morocco. Bar five paltry years in between, the border has been closed ever since. In 1963 the two countries fought a brief war. Skirmishes are now rare, but fighting words are common. Algerian republicans deride Morocco’s monarch as feudal, and because of the kingdom’s land-grab of Western Sahara call him the world’s last colonial ruler. Their neighbours cannot help sniggering at Algeria’s latest prime minister, whose name, Tebboune, is Moroccan slang for “vagina”.