In Roman mythology, Curtius was Marcus Curtius. In 445 BC, lightning struck near the Forum Romanum. The hole it created was called the Lacus Curtius. An oracle claimed that the hole, which severely disrupted the business at the Forum, could be closed by the most precious thing Rome had. Curtius, dressed in full armor and riding a fine horse, jumped into the hole, which then disappeared.
Livy VII, 6.
Alternately, the Lacus was named after Mettius Curtius, a Sabine horseman who rode into or fell into it while fighting against Romulus.
Still another version has it that Caius Curtius, a consul of 445 BC, consecrated the site after the lightning strike.