Malawi–Mozambique border

Portugal on the coast, Britain on the lake

Portugal was on the Mozambique coast from 1505, when it set up a trading post on the island of Mozambique. In the 16th century it pushed up the Zambezi and took the river ports of Sena and Tete.^[1]

British interest in the lands around Lake Nyasa, which Malawi's government calls Lake Malawi, grew out of the exploration and missionary work of David Livingstone. He first saw the lake in 1859, and British churches started mission work there two years later.^[1] Scottish merchants founded the African Lakes Corporation to trade in the area in 1878, and Britain appointed a consul for the lake districts in 1883.^[1]

In 1884 a British–Portuguese treaty said Portugal's claims on the Shire River would not go beyond where the Ruo joins it, but it was never ratified.^[1] In 1886 Portugal signed treaties with France and Germany that in effect recognised its claim to a continuous strip across Africa from Mozambique to Angola. Britain replied that it would only recognise claims backed by effective occupation, as the 1885 Berlin Conference had required.^[1] On 21 September 1889 Britain declared a protectorate over the Makololo, Yao and Machinga lands of the lake area.^[1]

The treaty of 1891

A first Anglo-Portuguese treaty, of 20 August 1890, failed ratification. A temporary agreement followed in November 1890, and the treaty that set the line was signed on 11 June 1891.^[1] It gave Portugal only the eastern shore of the lake from the German East Africa border south to latitude 13°30′S. From there the line cut southeast to Lake Chiuta and Lake Chilwa, followed the Ruo and the Shire rivers, and then ran along the watershed (the high ground dividing two river systems) between the Zambezi and the Shire, and between the Zambezi and the lake, north to the 14th parallel.^[1]

An annex to the treaty let Portugal lease land for landing and storing goods on the lake shore, and let Britain lease land at the Chinde mouth of the Zambezi for the same purpose. Both leases were cancelled in 1925.^[1] A further agreement in 1893 recognised that Likoma and Chizumulu, two islands in the lake, were in Britain's sphere.^[1]

“To the west [of Mozambique] by a line which, starting from the above mentioned frontier on Lake Nyasa, follows the eastern shore of the lake southwards as far as the parallel of latitude 13°30′ south…”^[1]

Marking and adjusting the line

British and Portuguese commissioners marked the line in 1899–1900, and the two governments provisionally confirmed their work, with some corrections, in 1906.^[1] An agreement of November 1911 put the border on the thalweg of the Malosa, Ruo and Shire rivers. The thalweg is the line of the deepest channel. The same agreement listed which river islands went to each side, based on how the rivers looked in 1908.^[1] Further corrections and new beacons between the Malosa and the lake were approved in 1920.^[1]

In places the border follows roads. Stretches of the main Lilongwe–Ncheu and Dedza–Ncheu roads form the line, with the road itself counted as part of Malawi. On the Blantyre–Tete road, a short stretch is counted as part of Mozambique.^[1]

1954: the lake is split

On 18 November 1954 Britain and Portugal signed an agreement that moved the lake border from the eastern shore to the median line, the line halfway between the two shores. That gave Mozambique 2,471 square miles (about 6,400 km²) of water.^[1] It also moved the line in Lake Chiuta, gave Mozambique about 2 square miles of land near Nsanje, and gave Nyasaland about 8 square miles in the Angonia area. Overall Portugal gained 2,496 square miles (about 6,460 km²), almost all of it water.^[1] The agreement carried out a preliminary exchange of notes of 21 January 1953, which dealt with Portuguese participation in the Shire Valley Project.^[1]

Likoma and Chizumulu lie on the Mozambican side of the median line, but Britain kept sovereignty over both islands and a belt of water two sea miles wide around each. Where Likoma is less than four miles from the mainland, the water between was split equally.^[1] That is why the map shows two small Malawian loops on the Mozambican side of the lake line.

A joint commission re-marked the land border from the lake–Zambezi watershed to the Shire and reported on 27 August 1956. An exchange of notes on 29 November 1963 made its report part of the 1954 agreement.^[1] Nyasaland became independent as Malawi on 6 July 1964. When IBS No. 112 was written in 1971, Portugal still treated Mozambique as part of Portugal.^[1]