The Sanctuary of Isis and Serapis, as well as one of the biggest ancient theaters still standing in Greece, can be found on the vast site of ancient Messene. Ancient Messene, whose history spans from the 4th century BC to the 4th century AD, became a living museum and a model for other sites when the buildings were rebuilt and the site was made public for events at Themelis' initiative. Its area is at least forty hectares.
Themelis, who was born in Thessaloniki in 1936, was the son of writer Giorgos Themelis. He obtained his doctorate from the University of Munich after studying history and archaeology at the University of Thessaloniki.He held a number of positions in the archaeological service, including head of ephorates in Attica and Evia, Fokida-Lokrida, Etoloakarnania, and Messinia and Ilia (all in Central Greece) from 1963 to 1980. From 1980 to 1984, he also oversaw the Ephorate of Paleoanthropology and Speleology. He oversaw the first phase of the excavations at Ancient Eleftherna, which is situated on Crete between Rethymno and Iraklio, (1985–2003), as well as the Delphi Museum (1977–1980). From 1986 until his death, he oversaw the excavations and restoration of Ancient Messene. In recognition of his efforts there, he was awarded the Europa Nostra prize twice, in Madrid in 2006 and Amsterdam in 2011. Among his other roles at the University of Crete, he taught classical archaeology from 1984 to 2003.
Ten monographs, two hundred reports, tour and site guides, and newspaper articles from Athens and Messinia were also published by Themelis. For his services, he was named an honorary citizen by Messini, Andritsena, and Kalamata. He was also a life member or honorary member of numerous Greek and international organizations.
President Kostis Stefanopoulos awarded him the Order of the Phoenix, Commander in 2005, and President Prokopis Pavlopoulos awarded him the Order of the Phoenix, Grand Commander in 2016.