Isidore’s Compass

A Scholium by Eutocius on Hero’s Treatise On Vaulting

In: Nuncius
Giangiacomo Martines Former Regional Director of the Ministry of Heritage, Cultural Activities and Tourism, in Friuli Venezia Giulia, Italy

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In the history of architecture, the construction of vaults was one of Rome’s supreme achievements, yet paradoxically it is not mentioned in any of the existing literary sources. Hero of Alexandria wrote a treatise entitled On Vaulting, which unfortunately is lost. A commentary on it was written by Isidore of Miletus, who lived at the time of the construction of the Hagia Sophia in Constantinople. We know this only from a brief remark in Commentary on the Sphere and Cylinder of Archimedes, written by Eutocius of Ascalon; furthermore the scholium refers to the drawing of a parabola. It was at about this same time that the parabola became very important in the East, as can be seen in the construction of Kosrow’s Arch at Ctesiphon. The present study examines Eutocius’ remark and the context in which it is to be found in his Commentary, and takes a look at the primacy of the parabola in the static behaviour of domes.

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