"the Stoic philosopher Euphrates"

Euphrates (35-118 AD) was a native of Tyre. He became a friend of Pliny the Younger, and is described by him in a letter to Atrius Clemens (Epistle I.10 - http://etext.lib.virginia.edu/toc/public/PliEpis.html). It is Cassius Dio (Roman Histories LXIX,8 - http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cassius_Dio/home.html), however, who tells us that he sought and obtained permission from Hadrian to end his life by poison.