The Five Brothers Bastion is located on the northwestern side of Akronafplia and was constructed to control the entrance to the port of Nafplio with Bourtzi.

The Five Brothers is a protruding section of wall from the rest of the Acronafplia wall, autonomously fortified to defend Nafplio from the Argolic Gulf side above the Sea Gate.

The construction of the Promachon dates from 1389-1540 when Nafplio was under the rule of the First Venetian Empire.

At that time there was also the discovery of gunpowder, so they put special emphasis on the defensive fortification technique of the bastion by placing five cannons of heavy type and from there it was named Five Brothers Bastion.

From the Promachon every night they spread a heavy chain to Bourtzi to block the entrance of Nafplio from the sea and thus gave the port of Nafplio the name Porto di Cadena.

The Five Brothers Canons preserved in good condition come from a factory in Venice by John Francis Almercetti that existed since 1487, and in one of the cannons of the bastion the cast, manufacturer left his signature MARCANTONIO Q. NICOLOL΄OR DIOCONDO D `ARTIGLIARIE.