On February 27, 1976, the Polisario Front formally proclaimed the Sahrawi Arab Democratic Republic and set up a government in exile, initiating a guerrilla war between the Polisario and Morocco, which continued until a 1991 cease-fire. As part of the 1991 peace accords, a referendum was to be held among indigenous people, giving them the option between independence or inclusion to Morocco. To date the referendum has not been held because of questions over who is eligible to vote. Ancient and classical antiquity Phoenician/Carthaginian colonies established or reinforced by Hanno the Navigator in the 5th century BC have vanished with virtually no trace. The desertification of the Sahara during the "transitional arid phase" ca. 300 BC - 300 AD" made contact with some parts with the outside world very difficult before the introduction of the camel into these areas, from the third century of the Christian era on. The camel was primarily used as a beast of burden; people walked beside them. Also camel meat, milk, and skin were important. The horse, not the camel, was the animal used in warfare in the period 1000–1500 AD ("the period of horse warriors and conquest states"). Contacts with Roman Empire Plinius wrote that the coastal area north of the river Senegal and south of the Atlas Mountains was populated, during Augustus times, by the Pharusii and Perorsi, What is now Western Sahara was a dry savanna area during classical antiquity, where independent tribes like the Pharusii and the Perorsi led a semi-nomadic life facing a growing desertification. Romans made explorations toward this area and probably reached, with Suetonius Paulinus, the area of Adrar. There is evidence (e.g., coins, fibulas) of Roman commerce in Akjoujt and Tamkartkart near Tichit. The western Sahara population (in those first centuries of the Roman Empire) consisted of nomads (mainly of the Sanhaja tribal confederation) in the plains and sedentary populations in river valleys, in oases, and in towns like Awdaghust Tichitt, Oualata, Taghaza, Timbuktu, Awlil, Azuki, and Tamdult. Some Berber tribes moved to Mauritania in the third and fourth century, and after the 13th century some Arabs entered the region as conquerors . Islamic era Islam arrived in the 8th century AD between the Berber population who inhabited the western part of the Sahara. The Islamic faith quickly expanded, brought by Arab immigrants, who initially only blended superficially with the population, mostly confining themselves to the cities