This article presents the Syriac Galen Palimpsest's double history, of both the original manuscript and its subsequent reuse. The original medical manuscript contained Galen's Book of Simple Drugs in Syriac translation, was probably produced in northern Mesopotamia or western Syria, and dates to the first half of the ninth century. After only two centuries, it was erased and reused to produce a liturgical text called Octṓēchos, probably at the monastery of Saint Elias on the Black Mountain. This palimpsest was later transferred to Saint Catherine's monastery in the Sinai, where it remained for several centuries before being offered for sale in Leipzig in 1922 (perhaps due to the activities of Friedrich Grote). We pay close attention to the context, contents, codicology and palaeography of both the original manuscript and the palimpsest. We also contextualise both texts within the wider story of their transmission. Through the "skeleton" table we present the latest results of our almost complete identification of the undertext. We reconstruct the structure of the original codex through a collation diagram. We draw palaeographical parallels with a dated colophon of the well-known Sahdona-manuscript. This permits us to narrow done the time and place of production of the original manuscript.