Magnesia

Magnesia may refer to:


 * Magnesia (hypothetical city), a future colony of Knossos, imagined in Plato's Laws
 * Magnesia (regional unit), the southeastern area of Thessaly in central Greece
 * Ancient Magnesia, a historical region of Greece with borders differing from the modern regional unit
 * Magnesia ad Sipylum, a city of Lydia, now Manisa in Turkey
 * Battle of Magnesia, 190 BC, the concluding battle of the Roman–Seleucid War
 * Magnesia on the Maeander, an ancient Greek city in Anatolia
 * Magnesia Prefecture, a former prefecture of Greece

Chemistry

 * Magnesium oxide
 * Periclase or magnesia, a natural mineral of magnesium oxide