Nicaea or Nikaia (Greek: Νικαία or Νίκαια) may be:

• The ancient name of several places, including:
  • Empire of Nicaea
  • Nicaea (city), capital of the Empire of Nicaea and known today as İznik, Turkey
  • Nice, France
  • Nicaea (Punjab), in the Punjab, built by Alexander the Great
  • Nicaea (Locris), a fortress city of the Locri Epicnemidii
• Nikaia, Attica, a suburb of Athens, Greece
• Nikaia, Larissa, a town in the Larissa Prefecture, Greece.

Nicaea may also refer to:

• The First Council of Nicaea in AD 325, the first ecumenical council of bishops of the Christian Church
• The Second Council of Nicaea in AD 787, the seventh ecumenical council of the Christian Church
• The Council of Nicaea (painting), an 18th century painting of the the first ecumenical council
• The Council of Nicaea (Doctor Who audio), a science-fiction audio drama
• Nicaea of Macedonia, daughter of Antipater

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