Areia Reef

Areia Reef lies in the coastal waters off the mouth of the São Francisco River, which reaches the Atlantic between the Alagoas and Sergipe coasts. The river connects the shore with a vast inland basin, and its lower course carried traffic between the sea and the interior.

Farther upriver, Penedo became a town in 1636. Dutch forces occupied it in 1637 and built Fort Maurício to secure access along the São Francisco. Fighting over the lower river shaped the struggle for northeastern Brazil, and the reef's waters belonged to that coast.