(The), strictly speaking, meant the place where Romulus and Remus were suckled by the wolf (lupus). A yearly festival was held on this spot on Feb. 15, in honour of Lupercus, the god of fertility. On one of these festivals Antony thrice offered to Julius Cæsar a kingly crown, but seeing the people were only half-hearted, Cæsar put it aside, saying, “Jupiter alone is king of Rome.” Shakespeare makes Antony allude to this incident:
You all did see that on the Lupercal I thrice presented him a kingly crown. Which he did thrice refuse.
Julius Caesar, iii. 2.
Shakespeare calls the Lupercalia “the feast of Lupercal” (act i. 1.), and probably he means the festival in Antony's speech, not the place where the festival was held.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894