In the middle of the southern side of the initial enceinte, which run along the modern Daidalou and Chandakos str., on the southern edge of the main street that crossed the city ending at the gate of the Mole, the modern avenue dedicated to the Martyrs of the 25^th of August 1898, was situated the main gate, the Gate of the Fortress or Gate of the Impost, as it was called during the Byzantine period. During the early Venetian period the gate was called Porta Maestra and it was flanked by two quadrangular towers. Its original place is estimated to have been by the corner of Daidalou str. and 25^th of August av. During the 15^th c. reinforcement of the enceinte, the gate was displaced shortly to the South and was flanked by a pair of towers in projection. Since the southern enceinte became much thicker after the addition of the bulwark, the gate received the form of a portico and a new name, Portone. A timber drawbridge, laying on corbels, which were revealed during an excavation in 1992, helped the transit between the gate and the opposite side of the moat.

Around the middle of the 16^th c. over the Portone was costructed a four-storey building, which hosted warehouses and a prison (fondaco vecchio). The gate, in its new imposing form, took the name Voltone. The over the ground section of the gate collapsed during the earthquake of 1856. The inclined bulwark between the towers, which was preserved almost intact under the ground, was revealed during excavations in 1992 and 2009 at a short distance to the South of the entrance of the public Library (“Vikelaia”), but it was backfilled once more. The projecting eastern flank-tower, on the top of which was built a hotel named “London” was demolished in the period 1921-1926 for the construction of the municipal mansion called “Achtarika”, which hosted the “Scientific Club” and the “Vikelaia Library”.

Recently, during the reinforcement of the building’s foundation, the inner surface of the southern inclining masonry of the tower was revealed and can be visited in the basement of the building. From the coats of arms of the officials that were responsible for the construction of the tower only two have survived, those of the general Fantino Zorzi and the counselor Giovanni Moro, today in the Museum for the Cretan History. The western tower was demolished in 1960 to be replaced by a modern building block.