Peñón of Algiers ("El Peñón de Argel") refers to a small islet off the coast of Algiers, fortified by the Kingdom of Spain during the 16th century. The islet was connected to the African continent to form a seawall and the harbour of Algiers.
Peñón of Algiers Wikipedia
Established in 1510 when the Spaniards settled on a small island in front of Algiers (modern Algeria), the Peñón of Algiers enforced Sālim al-Tūmī (Selim-bin-Teumi) to observe the terms of a treaty with Spain to accept a Spanish presence and to pay tribute. Fortifications were built on the islet, and a garrison of 200 men was established. Sālim al-Tūmī had to go to Spain to take an oath of obedience to Ferdinand of Aragon.
The islet was captured in 1529 by Hayreddin Barbarossa in the Capture of Algiers (1529). Barbarossa dismantled the fortifications, ending the Spanish presence in the area.