Ancus Marcius was the fourth king of Rome, reigning from 642 to 617 BCE. He was known for his efforts to expand the city and improve its infrastructure. Ancus is credited with founding the port of Ostia, which helped facilitate trade and commerce for the growing city. In addition to his focus on expansion, Ancus Marcius also emphasized religious and cultural development. He is believed to have established several important religious institutions and rituals, further solidifying the role of religion in Roman society. His reign is often seen as a time of growth and stability for early Rome.