The field of Classics covers the languages and literatures of ancient Greece and Rome and their historical contexts. Chronologically, this is a wide field, extending from roughly the eighth century BCE (Before the Common Era) to the third or fourth century CE (Common Era). While the geographic center may be the Italian peninsula and Greece, the Mediterranean basin is also part of the field of study.
The Oxford Classical Dictionary (4th ed., 2012) is the basic quick reference source in Classics. The OCD, 3rd rev. ed., Main Reference DE5 O9 2003 is still a useful reference tool.
The Classical Studies subject section of Oxford Reference provides access to additional reference sources.
The Encyclopedia of Ancient History offers comprehensive scholarly coverage of the ancient Mediterranean world.