"At Odessos a trader returning from a voyage of several years' time made me a present of a green stone "

Yourcenar presumably means jade, which would have come from China or south-east Asia, and uses this as a spur for Hadrian to reflect on what might lie beyond the limits of the known world. In fact, no imported objects of jade have ever been found in a Roman context, but indirect trade did take place: Roman glass has been found on Chinese sites and Pliny the Elder, among other Roman writers, refers to the popularity of silk as a fashion accessory in Rome. The Chinese historical text, Hou Hanshu, refers to a Roman diplomatic delegation arriving at the court of Emperor Huan in 166 AD, sent by a ruler named "Andun" (安敦 in Chinese) usually thought to refer either to Antoninus Pius, Hadrian's immediate successor, or to the recipient of Yourcenar's fictional letter, Marcus Aurelius).