All that remains of the original Frankish fortifications are two enclosures, one external and one internal, the donjon and few other traces, as down the centuries both the Byzantines and the Ottomans constantly adapted them to meet the needs of war.

New walls were erected when the settlement was founded some time after 1262, originally so as to include the nobles’ houses and the despots’ palaces in the upper city, and later the remaining houses and monasteries in the lower city, also known as Mesochora. The first Frankish enclosure began to the north-west of the castle, descended to enclose the central plateau where the palaces were built, and then ran to the south, above Pandanassa, to the edge of the rock above the precipice. The second enclosure was probably founded in the 14th century; it began above Aphentiko and ran below the Cathedral to reach Peribleptos. The upper and the lower cities were linked to each other via what is now known as the Monemvasia Gate, and with the outside world via the so-called Anapliou Gate. A rampart was later built in front of this, creating a broad open space in front of the main wall. At this point the rampart and wall formed a special stronghold that effectively controlled the movement of people and goods in and out of the city.

The particular location of the monasteries dedicated to the Virgin Mary (Pantanassa in the eastern leg of the first enclosure, and two others on the edges of the second) indicate that the organization of the city fortifications provided for independent fortified points at the edges and the most vulnerable points of the settlement. It is perhaps no coincidence that the three monasteries were dedicated to the Virgin, as was Constantinople herself. The main entrance to Mesochora was known as the Marmara Gate; smaller gates have come to light or are thought to have existed at particular points in the settlement, close to monasteries or at the ends of small streets that originally led to the wall. The rectangular and round wall towers were built close to each other using strong rubble masonry interspersed with bricks, occasionally in a decorative mode or as free cloisonne masonry. They secured defence and remain impressive to the present day.