Cassandreia (Ancient Greek: Κασσάνδρεια - Kassandreia) was once one of the most important cities in Ancient Macedonia, founded by and named after Cassander in 316 BC. It was located on the site of the earlier Ancient Greek city of Potidaea, at the isthmus of the Pallene peninsula. The fact that Cassander named it after himself suggests that he may have intended it to be his capital, and if the canal which cuts the peninsula at this point was dug or at least planned in his time, he may have intended to develop his naval forces using it as a base with two harbours on the east and west sides. Cassandreia soon became a great and powerful city, surpassing the other Macedonian towns in wealth. Philip V of Macedon made Cassandreia his main naval base. At the end of the Roman Republic, a Roman colony was settled around 43 BC by the order of Brutus, by the proconsul Q. Hortensius Hortatus. The official name of the colony was Colonia Iulia Augusta Cassandrensis. The colony enjoyed ius Italicum, and is mentioned in Pliny the Elder's encyclopaedia and in inscriptions. It was destroyed by the Huns and Slavs around 540 AD.
The Christian diocese based on the ancient town is mentioned in the early 10th-century Notitiae Episcopatuum of Byzantine Emperor Leo VI the Wise. Its bishop Hermogenes participated in both the Robber Council of Ephesus in 549 and the Council of Chalcedon in 551. No longer a residential bishopric, Cassandria is today listed by the Catholic Church as a titular see.
- POTEIDAIA (Nea Poteidaia) Chalkidike, Greece, entry in The Princeton Encyclopedia of Classical Sites.
- Smith, William, ed. (1854–1857). "Cassandreia". Dictionary of Greek and Roman Geography. London: John Murray.
- Pliny the Elder, Natural History Book 4 Chapter 17
- Michel Lequien, Oriens christianus in quatuor Patriarchatus digestus, Paris 1740, Vol. II, coll. 77-78
- Pius Bonifacius Gams, Series episcoporum Ecclesiae Catholicae, Leipzig 1931, p. 429
- Annuario Pontificio 2013 (Libreria Editrice Vaticana 2013 ISBN 978-88-209-9070-1), p. 860
- F. Papazoglou, Les villes de Macédoine à l'époque romaine, Supplément du BCH 16, Athens, 1988.
- D. Samsaris, La colonie romaine de Cassandréa en Macédoine. Colonia Iulia Augusta Cassandrensis (The Roman Colony of Cassandra in Macedonia. Colonia Iulia Augusta Cassandrensis). Dodona 16(1), 1987, 353-437.
- John R. Melville-Jones, 'L'ixola di Caxandria' in Thesaurismata 27, 1997, 125-138.