The Minoan Invention
True Dome and Arch:
W. Sheppard Baird
December 11, 2012
If you believe the Early Minoan tholos tombs were free-standing, above-ground domes fully vaulted
in stone as many now do given the evidence of the relatively well preserved Tholos Tomb Gamma from
the Archanes cemetery of Phourni (Sakellarakis, 1997) and the extensive collection of Bronze Age
tholos structures found throughout the Mediterranean in the Aegean, Spain, Sardinia, etc. that are
still standing then it has to be recognized that these masonry structures must adhere to the
equilibrium and stability principles of modern architecture.
Pylos Tholos Tomb - c. 1550 BC
Messinia, Peloponnese, Greece
Credit: Dan Diffendale
In 1675 the English scientist and architect Robert Hooke was the first in historical times to describe
what became known as the ideal "Catenary" form for an arch (or a dome which is simply a three dimensional
arch created by rotating it about its central axis) by intuitively coining the phrase - “As hangs the
flexible line, so but inverted will stand the rigid arch” or in more modern terms - "As the chain hangs
in tension, the arch stands in compression". Johann Bernoulli, Gottfried Leibniz, and Christiaan Huygens
each independently derived the mathematical properties of this perfect catenary form and all three of
their solutions were published in the Leipzig scientific journal Acta Eruditorum in 1691 the result of
which is the general Cartesian equation: f(x) = a cosh (x/a).
Hanging String of Beads
Forming Two Catenary Curves
"Hooke’s insight is confirmed by the modern ‘safe theorem’ of the plastic theory of design. The laws
of static equilibrium are paramount; the theorem states that if a set of internal forces in a masonry
structure can be found that equilibrate the external loads, and which lie everywhere within the
masonry, then the structure is safe – safe in the sense that it cannot collapse under those
loads." (Heyman, 1999).
The catenary profile is the ideal mathematical form of arch for bearing a maximum of weight with the least amount of material. For any given arch, vault, or dome the resultant "lines of thrust" due to its weight and loading always take the shape of the inverted catenary. Therefore the optimal design of any arch should be one derived from a catenary form. This is exactly what was done with the Canaanite Fortification gate in the Mediterranean seaport of Ashkelon on the Levantine coast in the 19th or 20th century BC.
Bronze Age Ashkelon Fortification Gate
a True Arch with Catenary Analysis
Recently another arched gate that obviously incorporates the catenary form has been discovered at the
Bronze Age Argaric La Bastida site in Murcia, Spain which is claimed to be somewhat older than the
Ashkelon gate. The top of this arch obviously could not have supported itself during construction and
almost certainly some kind of falsework (wooden form, etc.) was used to hold the stones in place until
the mortar fully set. Therefore it is not a corbelled arch like the well-dressed Ugarit postern gate
which was built by simply stacking and cantilevering stone allowing it to be self-supporting during
construction. The Argaric postern gate at La Bastida is doubtlessly a "true" arch in the fully modern
Ugarit Postern Gate - A Corbelled False Arch
Credit: Wikipedia, Disdero, 2008
Argaric La Bastida Catenary Arched Gate - A True Arch
Credit: ASOME-UAB 2012
W. Sheppard Baird, 2011, The Garlo Well Temple and Tholos Structural Mechanics
Bernoulli, J., 1691-92, "Lectures on the Integral Calculus", Translation by William A. Ferguson, 2004.
Besenval, R., 1984, Technologie de la voûte dans l'Orient Ancien. 2 vols.Paris: Editions Recherche sur les Civilisations.
Gregory, D., 1697, Catenaria. Philosophical Transactions of the Royal Society 19, 231: 637–652.
Heyman, J., 1966, The Stone Skeleton. International Journal of Solids and Structures 2: 249–79.
Heyman, J., 1995, The Stone Skeleton. Structural Engineering of Masonry Architecture. Cambridge: Cambridge University Press.
Heyman, J., 1998, Structural analysis: a historical approach. Cambridge: Cambridge University Press.
Heyman, J., 1999, The Science of Structural Engineering. London: Imperial College Press.
Hooke, R., 1675, A description of helioscopes, and some other instruments. London.
Huerta, S., 2003, El cálculo de estructuras en la obra de Gaudí. Ingeniería Civil 130: 121–33.
Huerta, S., 2004, Arcos, bóvedas y cúpulas. Geometría y equilibrio en el cálculo tradicional de estructuras de fábrica. Madrid: Instituto Juan de Herrera.
Huerta, S., 2006, Galileo was Wrong, The Geometrical Design of Masonry Arches
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