Jonas hill and the Citys Bastion Fortifications
Under the guidance of the engineer Charles Rose, the city was begun to be encircled in the manner of Holland-type fortifications, eastward from the former St. Johns church. Moulds and bastions measuring about 3.5 meters high were formed, and outer ditches (fosses) were dug. Because of their size, the city fortifications are categorized as being amongst the great royal castles. The works were finished in only the late 17th century-early 18th century. Later, the moulds were reconstructed in the mid-18th century. The fortification system of Klaipėda at that time was complex. Because the city was surrounded with bastion fortifications from the East and South, and secured by the Naujoji Danė River from the North, the only access was via three gates: named after their objects - Tiltas (Bridge), Kūlių (of Stones), and Malūnų (of the Mills). The latter two were built upon earthen ramparts.
During the wars in the 18th century, the maintenance of the fortress was neglected, the gateways were begun to be disassembled for their bricks, ramparts were torn-up, ditches were filled with soil, and in the 20th century only small fragments of the former complex fortification system remained.
Today, the former fortification system can be best observed at the end of Turgaus Street, from the bastions referred to in the historical records as the Geldern and Purmark. In front of the bastions can be seen the water-area of the defensive ditch/Foss, and the only surviving ravelin. The remains of these defensive fortifications were restored (author of project V. Šliogeris) in 1994-1997.
More information: http://www.klaipedainfo.lt