Woodblock frontispiece from the Diamond Sutra, printed during the Tang Dynasty, and considered—by Wikipedia and the British Library—to be the oldest dated printed book in the world. Dated to the year AD 604; (868.).
We clearly see in this woodcut the use of a pseudo-hexagonal background matrix of some sort. This is perhaps an allusion not only to the hexagonal structure of diamond itself, but also to the adamantine nature of hexagonal geometry.