Proper noun

Singular Ancient Greece

Plural -

Ancient Greece

1. The Greek speaking world in ancient times, geographically referring not only to modern Greece and southern Balkan peninsula but also to areas of Hellenic culture that were settled during ancient times by Greeks: Cyprus, the Aegean coast of Ionia, southern Italian peninsula and Sicily (known as Magna Graecia) and the scattered Greek settlements on the coasts of what are now Albania, Bulgaria, Egypt, Libya, southern France, southern Spain, Catalonia, Georgia, Romania, and Ukraine.
2. The civilization that flourished around the Mediterranean Sea from the 3rd millennium to the 1st century BCE (including the first two European civilizations, Minoan and Mycenaean), known as the cradle of Western civilization.

Ancient Greece is the civilization belonging to the period of Greek history lasting from the Archaic period of the 8th to 6th centuries BC to 146 BC and the Roman conquest of Greece after the Battle of Corinth. At the center of this time period is Classical Greece, which flourished during the 5th to 4th centuries BC, at first under Athenian leadership successfully repelling the military threat of Persian invasion. The Athenian Golden Age ends with the defeat of Athens at the hands of Sparta in the Peloponnesian War in 404 BC.

Classical Greek culture had a powerful influence on the Roman Empire, which carried a version of it to many parts of the Mediterranean region and Europe, for which reason Classical Greece is generally considered to be the seminal culture which provided the foundation of Western civilization.