Thermoluminescence Analysis of Bricks from the so-called Arch of Ali Shah

Abstract

The application of Thermally (TL) and Optically (OSL) Stimulated Luminescence on bricks used as building material can answer questions regarding the chronology of historical buildings. The remarkable historical reports of the “largest ever made brick vault” known as the Arch of Ali Shah (14th century) invoke the image of a gigantic structure adjoining the u-shaped brick monument in Tabriz. However, there is new scientific data that has led us to consider an alternate hypothesis regarding this monument that contradicts the traditional views of scholars. The attribution of this controversial building to Ali Shah, the great vizier of the Ilkhanid court, has long been considered an historical fact by scholars. To better understand the evolution of this unique structure, thermoluminescence (TL) was used to propose a relative dating for its construction. Surprisingly, the results yielded dates of 512±20, 514±27 and 517±21 AD (TL age, equaling 17th century), indicating that the u-shaped structure was built some 200 years after the Ilkhanid era. These dates, supplemented with historical context and architectural evidence, leads to the conclusion that it was used as a separate building before being integrated into the older building, thereby converting the entire complex into a formidable fortification. The remains of the so called Arch of Ali Shah are clearly of a later date, characterizing a completely different architectural style than those of the Ilkhanid period.