Ancus Marcius (Classical Latin: [ˈaŋkʊs ˈmaːrkiʊs]) was the legendary fourth king of Rome,[1][2][3] who traditionally reigned 24 years.

[5] Ancus is said to have ruled by waging war as Romulus did, while also promoting peace and religion as Numa Pompilius did.

According to Livy, Ancus's first act as king was to order the Pontifex Maximus to copy the text concerning the performance of public ceremonies of religion from the commentaries of Numa Pompilius to be displayed to the public on wooden tablets, so that the rites of religion should no longer be neglected or improperly performed.

[15] According to Livy, the accession of Ancus emboldened the Latin League, who assumed that the new king would follow the pious pursuit of peace adopted by his grandfather, Numa Pompilius.

Livy says that this event was notable as the first time that the Romans declared war by means of the rites of the fetials.

Its residents were removed to settle on the Aventine Hill in Rome as new citizens, following the Roman traditions from wars with the Sabines and Albans.

More Latins were brought to Rome as citizens and were settled at the foot of the Aventine near the Palatine Hill, by the temple of Murcia.