Cosmao was the third and final member of the Troude class of protected cruisers built for the French Navy in the late 1880s and early 1890s. The class was built as part of a construction program intended to provide scouts for the main battle fleet. They were based on the preceding Forbin class, the primary improvement being the addition of armor to the conning tower. Cosmao was built in the 1880s and was completed in 1890. She was armed with a main battery of four 138 mm (5.4 in) guns, protected with an armor deck that was 41 mm (1.6 in) thick, and had a top speed of 20.5 knots (38.0 km/h; 23.6 mph).