Titus Livius (Livy), The History of Rome, Book 1
Rev. Canon Roberts, Ed.

39. At¹ that time an incident took place as marvellous in the appearance as it proved in the result. It is said that whilst a boy named Servius Tullius was asleep, his head was enveloped in flames, before the eyes of many who were present. [2] The cry which broke out at such a marvellous sight aroused the royal family, and when one of the domestics was bringing water to quench the flames the queen stopped him, and after calming the excitement forbade the boy to be disturbed until he awoke of his own accord. Presently he did so, and the flames disappeared. [3] Then Tanaquil took her husband aside and said to him, ‘Do you see this boy, whom we are bringing up in such a humble style? You may be certain that he will one day be a light to us in trouble and perplexity, and a protection to our tottering house. Let us henceforth bring up with all care and indulgence one who will be the source of measureless glory to the State and to ourselves.’ [4] From this time the boy began to be treated as their child and trained in those accomplishments by which characters are stimulated to the pursuit of a great destiny. The task was an easy one, for it was carrying out the will of the gods. The youth turned out to be of a truly kingly disposition, and when search was made for a son-in-law to Tarquinius, none of the Roman youths could be compared with him in any respect, so the king betrothed his daughter to him. [5] The bestowal of this great honour upon him, whatever the reason for it, forbids our believing that he was the son of a slave, and, in his boyhood, a slave himself. I am more inclined to the opinion of those who say that in the capture of Corniculum, Servius Tullius, the leading man of that city, was killed, and his wife, who was about to become a mother, was recognised amongst the other captive women, and in consequence of her high rank was exempted from servitude by the Roman queen, and gave birth to a son in the house of Priscus Tarquinius. [6] This kind treatment strengthened the intimacy between the women and the boy brought up as he was from infancy in the royal household was held in affection and honour. It was the fate of his mother who fell into the hands of the enemy when her native city was taken that made people think he was the son of a slave.