Ghiyâth al-Dîn Jamshîd Kâshânî (al-Kâshî) is the prominent mathematician and astronomer of ninth/fifteenth century of Islamic civilization who founded the scientific methodology in practical and theoretical knowledge of mathematics in architecture. He played a significant role in the interaction and concurrence among mathematicians and architects, by addressing the relation between architecture and mathematics in two areas of knowledge, theoretical and practical, the latter itself including theoretical practice and practical practice. This paper addresses the question of how Kâshânî’s research has led to the foundation of the first theoretical basis for the application of mathematics in architecture in the form of easily practicable solutions for drawing, and measuring different types of ceilings, arches, vaults, domes, and ornaments, as well as estimating required materials. Further, we will discuss how his knowledge in mathematics and astronomy were utilized in management, design and construction of Samarkand observatory and its astronomical instruments. By exploring how the mathematical knowledge of a Persian scientist was utilized in architecture and craftsmanship, we will shed some light on the hidden layers of Kâshânî’s architectural life, who until now has been considered only a mathematician and astronomer.

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