To make an arch, the Romans built a wooden framework shaped like a half circle, on top
of which they put wedged stones (called "voussoirs"). They placed the stones starting at
The last stone (the "keystone"), located at the top of the arch, held the others in place.
The strength of an arch comes from its shape. When a load is placed on top of an arch,
its force spreads out and down the sides of the arch. At the ground, strong supports
("abutments") keep the arch from moving outward.
Ljubljana. Photo credit L.Babic
Ljubljana. Photo credit L.Babic
Legend has it that in ancient Rome, whenever an arch was constructed, the architect who
designed it was forced to stand underneath as the wooden supports were removed as a
means of quality control. It was a terrific motivational tool: design it right, or the arch
falls and crushes you.
The Romans were great engineers and were able to construct large structures such as
aqueducts very accurately. The Romans used aqueducts to transport water across valleys
to towns. Aqueducts must have a slight incline (angle) in order that the water flows down
hill, by the force of gravity. The Romans were capable of building to a consistent
accuracy over long distances.
Pont du Gard
Because of its tremendous strength under compressive forces, stone can bear an almost
unlimited load when arranged in the form of an arch. The ancient Romans used stone
arches for large bridges and aqueducts, and the tradition of building bridges in stone
continued in medieval and Renaissance Europe.
Stone bridges cost far more than comparably sized wooden bridges. Towns built them
only on their most important roads.
Stone bridges could be built with locally available skills. Carpenters were needed for the
arched-shaped wooden forms or centerings upon which the stones were laid, and
masons, who laid the stone.
The above photo is an unkown bridge being built somewhere in eastern Connecticut, USA
Builders have diverted the stream with a small dam, called a coffer dam, and then
excavated to bedrock to lay the first stones of the arch. Although irregularly shaped
pieces of stone were used, with no mortar, the stones were chosen carefully so that long
pieces tied together the masonry as the arch rose.
A centering was planked over to form a support for the arch, as it increasingly
approached a horizontal position.
Solkan bridge is one of the most famous bridges in Slovenia. It is one of the bridges on
the Bohinj Railway route between Jesenice and Gorica. According to the known data, the
bridge has the longest stone arch (85 metres) among all railway bridges.
< The Solkan Bridge
Rivers divide people, bridges bring them together: For almost 500 years, the old Bridge
of Mostar connected the lives of Christians and Muslims in an ancient town between the
Balkans and Europe.
To many, this masterpiece of mediaeval masonry
was as important as the leaning tower of Pisa or
the Acropolis in Athens. Built to equal halves by
Muslim and Christian craftsmen, the highest and
biggest stone-arch of its time stood as a symbol of
understanding between cultures.
Then came November 9, 1993: When war tore
former Yugoslavia apart, the age-old bridge was
destroyed by Croatian artillery. It left a wound that
has not healed to the present day.
Many of the old bridge-builders' secrets have long
been lost: How did they create a mortar that was
much harder than any mixture known today? And
how did they build a bridge that lasted 500 years
with stones that today's experts find not strong
< Old Bridge of Mostar
THE CORBELLED ARCH
Or false arch is another primitive structure. It is only a slight improvement over post and