‘A history of blood’ considers why the colour red and blood hold such pre-eminence in human language and culture. Views about what function blood actually performed in the body have varied widely through history. The studies of 2nd-century physician Galen are described along with procedures such as bloodletting, used in medicine for a long time. The structure of the vessels that contain blood in the body—arteries and veins—has always intrigued scholars. The 13th-century Islamic physician Ibn al-Nafis was the first to propose a circulatory system, but it was in 1628, when William Harvey, physician to King James I, published his findings, that the true circulatory system was explained.