Baghdad surrenders to the Mongol army

Baghdad's planned circular form joined surveying, geometry, architecture and imperial symbolism in a major urban project.

Al-Azhar opened in Fatimid Cairo and developed into a long-lived institution of learning.

Alongside religious and linguistic studies, scholars taught inheritance arithmetic, astronomy, timekeeping and related mathematical subjects.

Al-Azhar shows how mathematics was transmitted through teaching communities rather than only through famous books and individuals.

Students from Africa, Asia and the wider Islamic world carried methods and texts across linguistic and political boundaries.

Libraries and institutions suffered catastrophic loss, although the familiar story that all books were thrown into the Tigris cannot be treated as a precise inventory.

Knowledge survived through manuscripts and scholars in Maragha, Damascus, Cairo, Central Asia and other centers, preventing a simple rise-and-collapse narrative.

The destruction of Abbasid institutions redirected scholars and resources, reshaping rather than ending mathematics in the Islamic world.

Pope Gregory XIII issued the bull Inter gravissimas. It reformed leap-year rules to bring the civil calendar closer to the solar year.

The reform used astronomical calculation and a revised leap-year cycle to limit the drift of the equinox through the calendar.