[1][2][3] The situation in the region of Mansomine, north of the Geba River, was tense, with two enemy villages resisting Portuguese expansion.

He gathered a small force of 20 marksmen, 70 native auxiliaries, five traders, and a single artillery piece before marching from Geba towards Umbucu in July 1886, who commanded 180 men to defend the border.

The small village of Mansomine was fortified with large tree roots forming natural walls, and a moat surrounded it.

Meanwhile, the rest of the force, commanded by traders João José Rosa and Domingos Gomes Araújo, flanked the enemy through the woods and crossed the lagoon at a shallow point.

[3] The victory at Mansomine encouraged Geraldes, who proposed a combined operation to further secure the river's trade routes.