Africa has so many straight-line borders because European governments divided much of the continent on paper between the 1880s and the early 1900s, often before any surveyor had seen the ground, and a line of latitude, a meridian or a ruler-drawn segment between two known points was the easiest boundary to agree. The longest of these lines run through the Sahara and the Kalahari, where there were few rivers, towns or mapped features to follow: Egypt and Sudan are divided by the 22nd parallel, Egypt and Libya for much of their length by the 25th meridian east, and Mali and Mauritania by a single straight segment of about 955 km. The lines matter because the land they cross was not empty. They run through the grazing grounds, wells and oases of Tuareg, Toubou, Ababda and Maasai herders, and they have produced odd leftovers such as Bir Tawil, the patch of desert that neither Egypt nor Sudan claims.
The Berlin Conference of November 1884 to February 1885 is usually blamed, but it set rules for claiming territory rather than drawing most borders. A 2024 study found that the only boundaries it actually fixed were those around the Congo, which were later revised, and that most African borders took their final shape more than two decades afterwards through bilateral treaties. Those later treaties are where the ruler lines come from.
The 22nd Parallel Across Nubia
The Egypt–Sudan border runs about 1,276 km from the Libyan tripoint on the mountain of Gabal El Uweinat to the Red Sea. It was born on 19 January 1899, when an Anglo-Egyptian agreement defined Sudan as the territories south of the 22nd parallel. That line crosses the Libyan and Nubian deserts, a region with almost no settled population except along the Nile. There, the ruler line ran straight through Nubia, a region whose history had been bound up with Egypt’s since antiquity.
The river forced the first exception within weeks. On 26 March 1899 a salient north of the parallel was given to Sudan so that the railway from Khartoum could terminate under Sudanese control at Wadi Halfa. The town receives a mean of about 0.5 mm of rain a year, and the Nubian antiquities around it were the focus of rescue excavations before Lake Nasser rose behind the Aswan High Dam. Its population was 15,725 in 2007.
A second exception followed in the east. On 4 November 1902 the British drew an “administrative boundary” meant to reflect how tribes actually used the land. Bir Tawil, grazing land used by the Ababda people from near Aswan, went under Egyptian administration; the Halaib Triangle on the Red Sea coast, whose people were culturally closer to Khartoum, went under Sudan. Egypt now claims the 1899 parallel and Sudan the 1902 line, so both claim Halaib’s 20,580 km², which Egypt moved to take over in 1994 and has administered alone since Sudan withdrew its forces in 2000, and neither claims the 2,060 km² of Bir Tawil.
Down the 25th Meridian Through the Great Sand Sea
West of the Nile the grid turns north. The Egypt–Libya border, 1,115 km long, begins on the Mediterranean at the Gulf of Sallum and follows a series of irregular lines inland until it reaches the 25th meridian east. From there it runs due south to Gabal El Uweinat, the single mountain where Egypt, Libya and Sudan meet. Only the coastal strip in the north holds any real towns. The rest crosses the Great Sand Sea and the Libyan Desert, remote dune country with no significant population centres along the line.
Tibesti and the Toubou: The Chad–Libya Line
The Chad–Libya border is made of just two straight segments: about 113 km from the Niger tripoint up to the Tropic of Cancer, then 942 km southeast to Sudan. Together they cut across the Tibesti Mountains, a range of volcanoes in the central Sahara, with the remote peak of Bikku Bitti just on the Libyan side.
These mountains are the homeland of the Toubou, whose name has been read as “man who lives in Tibesti” in Kanuri. They live in northern Chad, southern Libya, northeastern Niger and northwestern Sudan, as herders and nomads or as farmers near oases, and their society is organised by clans, each holding particular oases, pastures and wells. A straight line drawn across that pattern of ownership can leave one clan’s oases, pastures and wells in two different countries.
The line was also fought over. A Franco-Italian agreement of 1935 would have moved the Aouzou Strip, about 114,000 km² reaching some 100 km into Chad, to Italian Libya, but it was never ratified. Libya occupied the strip in 1973, and the dispute fed the Chadian–Libyan War. In February 1994 the International Court of Justice ruled 16 to 1 for Chad, and a UN observer group watched the Libyan withdrawal, completed by June that year. The straight colonial line survived intact.
The Sahara Grid of the Tuareg
West of Tibesti the borders become a grid of long segments. The Algeria–Mauritania border is a single 460 km line. The Algeria–Mali border continues it for about 752 km before bending along the wadis of Tin-Zaouatene. The Algeria–Niger border is three straight lines, the longest 552 km. The 2,236 km Mali–Mauritania border begins with 172 km along the 25th parallel north and then turns southeast for its 955 km segment; only in the far southwest do streams, and finally the Senegal River, take over. Algeria’s lines with Mauritania, Mali and Niger were not even treaties between states: two French officers, the commandant of Upper Senegal and Niger and the military commander of Algeria’s Département des Oasis, agreed them on 7 June 1905, and the Niamey Convention of June 1909 refined them. They became international frontiers only when Algeria won independence in 1962.
This is Tuareg country. The Tuareg, an Amazigh people of roughly 4 to 5 million, are traditionally nomadic pastoralists ranging from southwestern Libya across southern Algeria, Niger and Mali into Burkina Faso and northern Nigeria, and they have controlled several trans-Saharan trade routes. The grid left them as minorities in several states: about 2 million in Niger, around 11% of its population, and roughly 0.5 million, or 3%, in Mali. Major fighting between Tuareg rebels and both governments ended after the 1995 and 1996 agreements, but a new surge of violence came in Niger in 2007.
Kilimanjaro to Lake Victoria: The Line Through Maasai Country
In East Africa the ruler met greener land. In November 1886 Britain and Germany agreed on their spheres of interest along what is now the Kenya–Tanzania border, and the Heligoland–Zanzibar Treaty of 1 July 1890 confirmed the division. The line was surveyed by two British brothers. Charles Stewart Smith and George Edward Smith marked the 290 km from the coast to Mount Kilimanjaro in 1892, and twelve years later George returned to complete the remaining 480 km from Kilimanjaro to Lake Victoria, across open savanna and the Mara–Serengeti plains.
Those plains were, and are, Maasai grazing land. The Maasai are Nilotic pastoralists of Kenya and northern Tanzania, and Kenya’s 2019 census counted 1,189,522 of them. The border town of Namanga shows how the line sits on the land: it is split between Longido District in Tanzania and Kajiado County in Kenya, with Kilimanjaro in view, and lives on cross-border trade and tourists heading to Amboseli. Wildlife ignores the line altogether. Kenya’s Maasai Mara reserve is contiguous with Tanzania’s Serengeti, and the wildebeest of the Great Migration usually cross the Mara River from Tanzania in large numbers around July.
The Kalahari and the Caprivi Strip
The same 1890 treaty shaped the 1,544 km border between Botswana and Namibia. Most of it crosses the Kalahari, which covers about 70% of Botswana. The treaty text is a pure grid: from the south, the line follows the 20th meridian east up to the 22nd parallel south, runs east along it to the 21st meridian, north along that meridian to the 18th parallel, and east again to the Chobe River, dividing German South West Africa from the British Bechuanaland Protectorate. Its strangest piece is the Caprivi Strip, a panhandle of Namibian territory between 32 and 105 km wide that Germany took in 1890, under a treaty clause promising a strip at least twenty English miles wide, to reach the Zambezi and, it hoped, a route to its East African colony. The river turned out to be unnavigable because of Victoria Falls, about 65 km east of the strip. The strip ends at a near-quadripoint, where Botswana and Zambia share a border only about 150 m long at Kazungula.
People crossed this line under the worst circumstances. During the German campaign against the Herero in 1904–1908, many Herero fled into the Omaheke, a western arm of the Kalahari, where most died of thirst and starvation. Around 1,000 escaped into British Bechuanaland, among them the paramount chief Samuel Maharero, and Herero communities still live in Botswana today around Maun and in villages such as Sepopa and Etsha. Where the Caprivi border follows rivers rather than surveyed lines, it has needed courts: in December 1999 the International Court of Justice awarded the uninhabited island of Sedudu (Kasikili to Namibia), in the Chobe River, to Botswana after deciding that the “main channel” named in the 1890 treaty ran north of it.
After Independence: Why Africa Kept the Ruler Lines
At independence, African states overwhelmingly kept the boundaries they inherited, following the principle of uti possidetis juris, under which new states take over the colonial lines rather than reopen them. In both the Aouzou and Sedudu cases, the International Court of Justice settled the dispute by reading colonial-era treaties. The result is a map on which a Toubou clan’s wells, a Tuareg caravan route or a Maasai grazing range can sit in two or three countries at once. For the treaty-making that started the process, read about the Berlin Conference of 1884; for the wider pattern, see our guide to colonial legacy borders; and for the desert where most of these lines run, explore the geography of the Sahara.