Analysis of the surfaces of the walls and the building techniques and materials, showing up the restoration stages and the repair works

The first stage (1546-1564) of building the fortress under Domenico dell’Allio involved a fundamental change in the fortress system, which was made necessary because of the effect of the new firearms. Instead of the previous broken lines and angles, the new fortress technique favoured increasing protection against firing on the defence front by means of flankers, a principle that was used on late medieval town fortresses by projecting the wall towers and walkways outwards.
Prominent bastions were built instead of the wall towers. These were a lot lower and more spacious, so as to offer less surface area for attack from the heavy artillery of the besiegers on the one hand, and on the other hand to make it possible for the defenders to bring in more guns. The bastions were also a contrast to the walled towers, made of earthworks and only encased in brick walls on the outside. The ring wall between the town towers was replaced by an earth embankment, and the curtain walls, which were at the base as well as along the escarpment towards the town moat, were built with cut stone blocks. These contained the casemates, used as storage rooms for war material and as an enclosed protection for the occupying forces standing in the line of fire.
The new fortress technique paid particular attention to the moat, which was enlarged and made deeper, always taking into account the moment the water level was at its lowest and keeping it away from the tributary of the Mur. Earthworks were used all round as an earth bank in front of the town wall. The moat wall facing the enemy was often reinforced with stones. The outer borders of the moat had a rampart or dam in front, and were also of a zigzag pattern, like the recessed corners in the bastions, curtain walls and moat. A palisade was placed in front of the wall as an initial obstacle.
The building material was taken from the vicinity of the town. The stonework and bricks were brought in from Herzogberg and Poellitschberg. These were used to encase the curtain walls and bastions. In the beginning, stones from the derelict church of St. Ruprecht were also used. The limestone came from Halbenrain, Mureck and Hl. Dreikoenig. For the wall cornice and encasing, the master builders preferred the tough basalt from Kloech. The need for construction timber was covered by the sovereign and manorial woods in the surroundings.
Construction of the bastion at the upper gate (“Ungartor”, Ungarbastei”) began in 1547 in the north corner of the town. At about the same time the Bourgeoisie Bastion was worked on (both bastions were almost completed by 1550).
In the meantime, on the opposite side of the town, the town wall of the lower gate - the Murtor - was built as far as the tower of the Augustinian monastery, which had been badly damaged by fire (1549) and was in need of rapid restoration. After that, the building work was put on hold, because the houses damaged by fire had to be dealt with first.
In 1554, the fortification works were continued. At first the moat had to be cleared again and made deeper, then construction of the Mur Bastion started. In 1556, the big town gate (Murtor) was inserted into this bastion. Two years later dell’Allio went to construct a moat, “from the new bastion beside the town wall” up the Mur, while approximately 15 fathoms of the curtain wall fell, as well as the corner of the big “Fleischhackerturm” (butcher’s tower). An enormous flood damaged the work so severely in 1571 that the town wall collapsed in many places.
Between 1570 and 1591 the second construction stage of the fortress started, with the necessary restoration works. Ditches had to be cleared, bulwarks had to be fortified with walls, the rampart had to be made higher and the casemates had to be built with bricks and stones. All these works were completed in 1574. At the same time, the collapsed curtain wall had to be built up again and the church included in the fortress belt. Then works continued with construction of the Hollow Bastion (“Eckh am Ungartor”) (corner at the Ungar gate). The Oberradkersburger Schlossberg was without an earthwork and the walled base was too weak and in danger from flooding, which is why the corner of the Hollow Bastion was reinforced as a safety measure. Completion of the Ungartor was also undertaken, covering the roof and making an ammunition room above the opening of the gate.
The bastions were completed in the following years: in 1584, bastion No. 6 (Augustinian monastery - later the “devil’s hole” or Kapuziner Bastion), and some curtain walls, such as the last bastion - the Clergymen’s Bastion (bastion near the spire).
At the same time, the branch of the Mur was provided with weirs and the water from the Prentlhof-Muehlgang was led away to fill the town moat. These efforts proved quite useless because in 1589 the area on the west side of the town was devastated by a huge flood.
Although construction of the fortress was officially completed in 1591, damage caused by fire, flooding and other adverse weather conditions had to be repaired from time to time. The works also had to be adapted time and again to the latest fortress building techniques. Restoration and completion therefore lasted centuries. Only in the years from 1620 to 1633 were extensive repair works undertaken on the fortress.
In the following years and centuries there was no more expansion but only repair work. In 1690, the drawbridges over the town moat were moulded. Repair work on the fortress was done throughout the whole of the 18th century.