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

40. It was now about thirty-eight years since Tarquinius had begun to reign, and not only the king, but the Fathers and the commons too, held Servius Tullius in the very highest honour. [2] Now the two sons of Ancus had always considered it a great outrage that they had been ousted from their father's kingship by the crime of their guardian, and that Rome should be ruled by a stranger whose descent was derived from a race not only remote but actually not even Italian. [3] But their indignation was vastly increased by the prospect that even after Tarquinius' death the sovereignty would not revert to them, but, plunging down to yet baser depths, would fall into the hands of slaves; so that where, a hundred years before, Romulus, a god's son and himself a god, had borne sway, so long as he remained on earth, in that self-same state a slave and [p. 143]the son of a slave woman would be king. It would¹ be not only a general disgrace to the Roman name, but particularly to their own house, if during the lifetime of Ancus' sons it should be open not only to strangers, but even to slaves to rule over the Romans. [4] They therefore determined to repel that insult with the sword. But resentment at their wrong urged them rather against Tarquinius himself than against Servius, not only because the king, if he survived, would be more formidable to avenge the murder than a subject would be, but because if Servius should be dispatched it seemed probable that the kingdom would be inherited by whomsoever else Tarquinius might choose to be his son-in-law. For these reasons they laid their plot against the king himself. [5] Two very desperate shepherds were selected to do the deed. Armed with the rustic implements to which they were both accustomed, they feigned a brawl in the entrance-court of the palace and, making as much noise as possible, attracted the attention of all the royal attendants; then they appealed to the king, until their shouts were heard inside the palace and they were sent for and came before him. [6] At first each raised his voice and tried to shout the other down. Being repressed by the lictor and bidden to speak in turn, they finally ceased to interrupt each other, and one of them began to state his case, as they had planned beforehand. [7] While the king, intent upon the speaker, turned quite away from the other shepherd, the latter lifted his axe and brought it down upon his head. Then, leaving the weapon in the wound, they both ran out of doors.