“Pierced stones” are found on ancient quays. The piercing may be horizontal or vertical. These stones have sometimes all be taken as mooring devices, but it might be of interest to distinguish mooring rings and loading derricks.
The Torlonia relief below clearly shows a mooring ring with horizontal piercing and a mooring line. The unloading bridge with a man carrying an amphora is also clearly pictured.
Pompei’s Porta Marina hosts a quay with many similar pierced mooring stones:
Another mooring ring with horizontal piercing can be seen on the North coast of Leptis Magna (which proves, by the way, that ships came on this side, perhaps before construction of the port inside the estuary). Note also the tenon and mortise system to attach the block inside the quay.
Mooring stones with vertical piercing are found also, e.g. on the west quay of Leptis Magna and recently at Boca do Rio (Algarve). These are fairly light structures.
However, heavier structures are found also … Most goods had to be loaded/unloaded on men’s back. The heavier goods (e.g. wild animals in cages that transited through Leptis Magna on their way to Rome’s arenas) would perhaps require some kind of machinery.
According to Wikipedia “A derrick is a lifting device composed of one tower, or guyed mast (guy lines 8 on the sketch below), such as a pole which is hinged freely at the bottom. It is controlled by lines (2 & 7) powered by some means such as man-hauling or motors (6), so that the pole can move in all four directions. A line runs down and over its bottom with a hook on the end, like with a crane (1 & 5). It is commonly used in docks and on board ships”.
This typically marine lifting device is not mentioned by Vitruvius who was more interested in lifting devices used for construction of buildings (Vitruvius, de Architectura, 10, 2): “All devices described above can also be used for loading and unloading ships, some upright, others laid down on pieces of timber that are easy to move. One may also place the same cables and the same pulleys on the ground in order to pull ships out of the water”
The derrick is nevertheless an obvious concept for any sailor used to handle mast, boom and topping lift.
The main interest of a derrick is that it can turn the load laterally by means of the lateral lines (7 on the sketch above). The vertical force is taken over by the vertical mast resting on a strong support. The horizontal force induced by the cantilever is taken over by two guy lines (8) placed on the land side behind the mast in order not to hinder the lateral movement of the load.
The semi-circular shape at Leptis Magna is still a bit mysterious …
It is interesting to compare these derricks to the poles used to support the “velum” in amphitheatres. They can be seen in Rome and in Nimes (France):
- 240 poles of 450 x 550 mm for Rome’s Coliseum,
- 120 poles with diameter 300 mm Nimes’ arena.
See the mark of the poles on the wall and the clamp holes