Titus Livius (Livy), The History of Rome, Book 1
Benjamin Oliver Foster, Ph.D., Ed.

39. At this time there happened in the house of the king a portent which was remarkable alike in its manifestation and in its outcome. The story is that while a child named Servius Tullius lay sleeping, his head burst into flames in the sight of many. [2] The general outcry which so great a miracle called forth brought the king and queen to the place. One of the servants fetched water to quench the fire, but was checked by the queen, who stilled the uproar and commanded that the boy should not be disturbed until he awoke of himself. Soon afterwards sleep left him, and with it disappeared the flames. [3] Then, taking her husband aside, Tanaquil said: “Do you see this child whom we are bringing up in so humble a fashion? Be assured he will one day be a lamp to our dubious fortunes, and a protector to the royal house in the day of its distress. Let us therefore rear with all solicitude one who will lend high renown to the state and to our family.” [4] It is said that from that moment the boy began to be looked upon as a son, and to be trained in the studies by which men are inspired to bear themselves greatly. It was a thing easily accomplished, being the will of Heaven. The youth turned out to be of a truly royal nature, and when Tarquinius sought a son-in-law there was no other young Roman who could be at all compared to Servius; and the king accordingly betrothed his daughter to him. [5] This great honour, for whatever cause conferred on him, forbids us to suppose that [p. 141]his mother was a slave and that he himself had been¹ in a state of servitude as a child. I am rather of the opinion of those who say, that on the capture of Corniculum, when Servius Tullius, the chief man of that city, had been slain, his wife, who was great with child, had been recognized amongst the other captive women, and on the score of her unique nobility had been rescued from slavery by the Roman queen, and had brought forth her child at Rome in the house of Priscus Tarquinius; [6] in the sequel this act of generosity led to a growing intimacy between the women, and the boy, as one reared from childhood in the palace, was held in affection and esteem; it was his mother's misfortune, who by the capture of her native town came into the power of its enemies, which gave rise to the belief that Servius was born of a slave woman.