 He wrote a geographic treatise on the lands of the Celts which has since been lost, but which is referred to extensively (both directly and otherwise) in the works of Diodorus of Sicily, Strabo, Caesar and Tacitus' "Germania".Posidonius's extensive writings and lectures gave him authority as a scholar and made him famous everywhere in the Graeco-Roman world, and a school grew around him in Rhodes.His grandson Jason, who was the son of his daughter and Menekrates of Nysa, followed in his footsteps and continued Posidonius's school in Rhodes.