Magnesia is one of the regional units of Greece. It is part of the region of Thessaly. Its capital is the city of Volos. About 70% of the population …Magnesia is one of the regional units of Greece. It is part of the region of Thessaly. Its capital is the city of Volos. About 70% of the population of Magnesia live in the Greater Volos area, which is the second-largest city in Thessaly and the third busiest commercial port in Greece.