There are thirteen square pillars topped by head-and-shoulder busts marking the front boundary of the Sheldonian and erected when it was built in 1662–8. When the Old Ashmolean (now the Museum of the History of Science) was built next door in 1679–83, another four matching heads were carved to go in front of that.
The official name for such heads is “herms”; the original accounts describe these heads as “termains”; and some people call them philosophers. But Max Beerbohm in Zuleika Dobson called them “Emperors”, and that is the name that has stuck. Each head shows a different type of beard.
The present heads are the third set. The first set lasted 200 years, but by 1868 they were crumbling and new ones were erected; undergraduates, however, daubed these in paint, and the harsh cleaning they received caused them to wear badly, so that they could be described by John Betjeman (in his verse autobiography Summoned by Bells) as “the mouldering busts round the Sheldonian” when he came up in 1925.
Between 1970 and 1972 the sculptor Michael Black, with two assistants, carved thirteen new heads for the Sheldonian, copying the originals by referring to the Loggan engraving; later he did another four for the Museum of the History of Science. Each head took a minimum of thirty hours’ work.