Upaon Acu

Upaon-Açu is the great island between the bays and estuaries of the Maranhão coast. Its shores face the Atlantic and the mouths of rivers draining the interior. Tupinambá communities inhabited the island before European colonists established a fortified settlement there. The surrounding estuaries gave access to the mainland and its navigable waterways. Its position made the island a key point in the struggle for the northern coast of Brazil.

In 1612 the French founded Saint Louis as the centre of their short-lived colony of Equinoctial France. Portuguese forces captured the settlement in 1615 and renamed it São Luís. The Dutch seized the town in 1641, but Portuguese forces recovered it in 1644. From this base, colonial expansion continued along the rivers of Maranhão, including the Mearim and Itapecuru.