“
A Greco-Roman trispastos (three-pulley
crane), the simplest crane type (150kg load).
Product focus
A Greco-Roman pentaspastos (five-pulley
crane), a medium-sized variant (c. 450kg load). William George Armstrong, 1st Baron
Armstrong (1810–1900), was an English
industrialist and the effective founder of the
Armstrong Whitworth manufacturing empire.
Aristotle but likely written later (384–322 BCE).
The first documented use of compound pulleys
in a block and tackle system was by Archimedes,
who Plutarch reported used them to move an
entire warship. Archaeological records show
evidence for both lifting tongs and lewis irons
appearing on Greek temples no later than c. 515
BCE, with archaeologists regarding the holes
that indicate use of a lifting device as positive
evidence for the existence of the crane.
During the days of the Roman Empire,
construction activity soared, with the Greek
crane being adopted and further developed by
the Romans. The tripastos, the simplest of the
Roman cranes, comprised a single-beam jib, a
rope and a block containing three pulleys, giving it
a mechanical advantage of 3:1. The Romans also
used heavier cranes, such as the pentaspastos, which
had five pulleys, and the polyspastos, which had a
set of three by five pulleys and two to four masts, depending on maximum load, and could lift up to
three metric tonnes using a winch, or six metric
tonnes using a treadwheel, or magna rota. This
gave the polyspastos roughly 60 times the lifting
capability of the ramp system used to construct
the Egyptian pyramids.
With the fall of the Western Roman Empire,
crane technology fell into disuse in Western
Europe, and was only reintroduced in the
Middle Ages. In the mid-13th century, reference
to the treadwheel reappears in French literature
at around the same time the use of harbour
cranes was first documented. Comprising a
large wooden wheel turning around a central
shaft, the treadwheel crane had a rope running
through a pulley at the end of its lifting arm,
allowing the crane to lift or lower its load via
the rotation shortening or lengthening the rope.
These cranes were primarily used to construct
large castles and cathedrals, with the crane being
The word
‘excavator’ refers
to a specific class
of machine, one
that is available
in many forms:
stripping shovels,
walking draglines,
and bucket-wheel
excavators.”
Reconstruction of a 10.4m-high Roman polyspastos
powered by a treadwheel in Bonn, Germany.
32
JULY 2017
Reconstructed gantry crane of Brugge, operated by two
lateral treadwheels.