Karema sat at an unfortunate intersection. Lake Tanganyika formed the eastern edge of the Congo basin, and by the 1870s the slave and ivory trader Tippu Tip had built a private empire along the upper Congo to the west, funneling his goods toward Zanzibar on the Indian Ocean coast. One of the caravan routes ran past this shoreline. Into this landscape rode King Leopold II of Belgium, president of the International African Association founded in Brussels in September 1876. His Comite d'Etudes du Haut Congo, created in November 1878, was a mask for personal colonial ambition - the seed from which the Congo Free State would grow. In 1879 the Comite's men occupied Karema and renamed it Fort Leopold.

Captain Emile Storms took command in 1882 from Lieutenant Jerome Becker. Yassagula, the chief of the village of Karema, attacked the new station soon after Storms arrived. Becker counterattacked before leaving for home, put Yassagula's men to flight and destroyed the village. Yassagula submitted a few months later and became, by the stiff accounting of the colonial record, 'a reliable ally.' Storms expanded the post, planted vegetables, and in 1883 crossed the lake to found Mpala on the opposite shore - where the German scientist Richard Bohm, accompanying a later expedition, took two bullets in the leg. Then came the 1884-1885 Berlin Conference. European diplomats redrew Africa across a map they barely knew, assigning the east side of Tanganyika to German influence. Karema was now on the wrong side of the line. Leopold abandoned it.

Rather than hand the fort over, Leopold offered it to the White Fathers, the missionary society founded by the French archbishop Charles Lavigerie. Lavigerie accepted. His missionaries rebuilt Karema not as a colonial outpost but as a village of refuge, settling it with five hundred people they had ransomed from the slave caravans still passing through the region. To protect them, a former Papal Zouave named Leopold Louis Joubert arrived in November 1886, armed and determined. He stayed a few months, then crossed to Mpala. The mission needed builders and doctors more than soldiers. In 1889 Adrien Atiman arrived. He was born in what is now Mali, captured by slavers as a child, ransomed by the Fathers, and trained in medicine in Malta. He served as Karema's doctor for sixty-seven years, until 1956. The church was completed in 1890; the fortified mission house, still standing, was finished in 1893.

Lake Tanganyika is 673 kilometers long - the longest freshwater lake in the world - and for more than a century the only reliable way to move along it has been by boat. In 1913 German engineers shipped a 1,300-ton steamer to East Africa in pieces, hauled it overland through forest and savanna, and reassembled it on the lakeshore. They christened it the Graf von Gotzen and armed it as a troop transport. After the First World War changed the map once more, the British renamed the ship MV Liemba. Rebuilt and patched and refitted across generations, the same hull still runs the lake, calling at Karema on its weekly ferry route between Kigoma and Mpulungu. Passengers climb down into small boats to reach the shore; the Catholic mission runs a guesthouse. From Karema, Land Rovers bump inland toward Mpanda, the district center, along roads that turn to soup in the rainy season.

Today Karema is a fishing village. The mission continues, quieter now - the diocese moved its headquarters to Sumbawanga in 1969, and the big ecclesiastical energy that once made Karema a junior seminary has diffused. But the 1893 mission house still stands. Adrien Atiman is buried here. The descendants of the five hundred still fish the lake their ancestors reached after long walks in chains. When the Liemba blows its horn off the shore, the sound carries across water that has witnessed caravans, gunboats, empires, and, if the shipwrights keep patching her, perhaps another century of the same gray ship.