Ancus Marcius was the legendary fourth king of Rome, who traditionally reigned 24 years. Upon the death of the previous king, Tullus Hostilius, the Roman Senate appointed an interrex, who in turn called a session of the assembly of the people who elected the new king. Ancus is said to have ruled by waging war as Romulus did, while also promoting peace and religion as Numa Pompilius did.

The king of Rome was the ruler of the Roman Kingdom. According to legend, the first king of Rome was Romulus, who founded the city in 753 BC upon the Palatine Hill. Seven legendary kings are said to have ruled Rome until 509 BC, when the last king was overthrown. These kings ruled for an average of 35 years.