Plutarch, Publicola
Bernadotte Perrin, Ed.

13. While Tarquin was stirring up in Tuscany another war against the Romans, a thing of great portent is said to have happened. When Tarquin was still king, and had all but completed the temple of Jupiter Capitolinus, either in consequence of an oracle, or else of his own good pleasure, he commissioned certain Tuscan craftsmen of Veii to place upon its roof a chariot of terra cotta. Soon after this he was driven from his throne. [2] The Tuscans, however, modelled the chariot and put it in a furnace for firing, but the clay did not contract and shrink in the fire, as it usually does, when its moisture evaporates. Instead of this, it expanded and swelled and took on such size, strength, and hardness, that it could with difficulty be removed, even after the roof of the furnace had been taken off and its sides torn away. [3] To the seers, accordingly, this seemed a divine portent of prosperity and power for those who should possess the chariot, and the people of Veii determined not to give it up. When the Romans asked for it, they were told that it belonged to the Tarquins, not to those who had expelled the Tarquins. But a few days afterwards there were chariot races at Veii. Here the usual exciting spectacles were witnessed, but when the charioteer, with his garland on his head, was quietly driving his victorious chariot out of the race-course, [4] his horses took a sudden fright, upon no apparent occasion, but either by some divine ordering or by merest chance, and dashed off at the top of their speed towards Rome, charioteer and all. It was of no use for him to rein them in or try to calm them with his voice; he was whirled helplessly along until they reached the Capitol and threw him out there, at the gate now called Ratumena. The Veientines were amazed and terrified at this occurrence, and permitted the workmen to deliver their chariot.