The History of Rome (1.10.2-1.10.6)

The people of Caenina, Crustumerium, and Antemnae were the greatest sufferers; they thought Tatius and his Sabines were too slow in moving, so these three cities prepared to make war conjointly.

Such, however, were the impatience and anger of the Caeninensians that even the Crustuminians and Antemnates did not display enough energy for them, so the men of Caenina made an attack upon Roman territory on their own account.

Whilst they were scattered far and wide, pillaging and destroying, Romulus came upon them with an army, and after a brief encounter taught them that anger is futile without strength. He put them to a hasty flight, and following them up, killed their king and despoiled his body; then after slaying their leader took their city at the first assault.

He was no less anxious to display his achievements than he had been great in performing them, so, after leading his victorious army home, he mounted to the Capitol with the spoils of his dead foe borne before him on a frame constructed for the purpose. He hung them there on an oak, which the shepherds looked upon as a sacred tree, and at the same time marked out the site for the temple of Jupiter, and addressing the god by a new title, uttered the following invocation: “Jupiter Feretrius!

these arms taken from a king, I, Romulus a king and conqueror, bring to thee, and on this domain, whose bounds I have in will and purpose traced, I dedicate a temple to receive the spolia opima which posterity following my example shall bear hither, taken from the kings and generals of our foes slain in battle.”