An ancient monument associated with a cult of the dead, there were several explanations that sought to explain the significance of the site. The most common was that of Dionysius of Halicarnassus.
"In Rome there were many other heaven-sent portents, but the greatest of all was this: Near the middle of the Forum, they say, a cleft in the earth appeared of fathomless depth and it remained for many days. Pursuant to a decree of the senate, the men in charge of the Sibylline oracles consulted the books and reported that when the earth had received the things of greatest value to the Roman people it would not only close up, but would also send up a great abundance of all blessings for the future. When the emotion had made this announcement, everyone brought to the chasm the first-fruits of all the good things he thought the father land needed, not only cakes made of grain, but also the first-fruits of his money. Then a certain Marcus Curtius, who was accounted among the first of the youths because of his prudence and his prowess in war, sought admission to the senate and declared that of all blessings the finest thing number the one most essential to the Roman state was the valour of its men; if, therefore, the earth should receive some first-fruits of this and the one who offered it to the fatherland should do so voluntarily, the earth would send up many good men. Having said this and promised that he would not yield this distinction to anyone else, he girded on his arms and mounted his war-horse. And when the multitude in the city had gathered to witness the spectacle, he first prayed to the gods to fulfil the oracles and grant that many men like himself should be born to the Roman state; then, giving the horse free rein and applying the spurs, he hurled himself down the chasm. And after him were thrown down the chasm many victims, many fruits, much money, much fine apparel, and many first-fruits of all the different crafts, all at the public expense. And straightway the earth closed up" (Roman Antiquities, XIV.11.1-5).
He also relates that, during the war between Romulus and the Sabines, their leader Mettius Curtius rode his horse into a swamp and so escaped.
"For he himself stood his ground fighting and awaited Romulus as he approached; and there ensued a great and glorious engagement between the leaders themselves as they fell upon each other. But at last Curtius, having received many wounds and lost much blood, retired by degrees till he came to a deep lake in his rear which its difficult for him to make his way round, his enemies being massed on all sides of it, and impossible to pass through by reason of the quantity of mud on the marshy shore surrounding it and the depth of water that stood in the middle. When he came to the lake, he threw himself into the water, armed as he was, and Romulus, supposing that he would immediately perish in the lake, — moreover, it was not possible to pursue him through so much mud and water,— turned upon the rest of the Sabines. But Curtius with great difficulty got safely out of the lake after a time without losing his arms and was led away to the camp. This place is now filled up, but it is called from this incident the Lacus Curtius, being about in the middle of the Roman Forum" (Roman Antiquities, II.42.5-6).
The original relief (above) is in the Palazzo dei Conservatori; a copy marks the Lacus Curtius in the Forum.
