Synesius the Alchemist was a writer on alchemy who lived during the 3rd or 4th century CE in the late Roman Empire. He is a different person from the more well-known Synesius of Cyrene, a philosopher and bishop. The alchemist Synesius is a somewhat obscure figure, but according to modern scholars, he was likely part of the network of practitioners in Roman Egypt, probably in the city of Alexandria, which was a major center for alchemical study.

His only known surviving work is a commentary on an earlier text called the Book of Democritus. This earlier work was attributed to the philosopher Democritus, though scholars believe this attribution is false and part of a tradition of pseudonymous writing in alchemy. Synesius’s commentary explains and elaborates on the techniques and ideas from that foundational text.

Synesius is significant as a representative of the Greco-Egyptian alchemical tradition. His work helps historians understand how practical laboratory knowledge and theoretical ideas about transforming matter were preserved and discussed in late antiquity. Alongside other alchemists, his writings are crucial sources for the early history of chemistry, documenting a blend of hands-on experiment, philosophy, and religious thought.