Neptune is best known as the Roman god of the sea, but his oldest and most distinctly Roman domain was fresh water, the springs, streams and standing water on which farming and the city depended. His festival, the Neptunalia, fell on the twenty-third of July, at the height of summer when water was scarcest and most precious, and Romans built leafy shelters and drew water in a rite plainly aimed at the drought. Only through his thorough identification with the Greek Poseidon did Neptune acquire the wider portfolio for which he is now famous: lordship of the sea, of earthquakes, and of horses.
Neptune's oldest Roman temple, built after Rome's naval victory over Carthage in the First Punic War and standing near the Circus Flaminius, shows how quickly the god's maritime side developed once Rome became a sea power, even though the cult began, as the Neptunalia's midsummer date suggests, as a plea against drought rather than a prayer for calm seas. Equestrian games held at his festival tie him to the domain of horses that later, through the Greek Poseidon Hippios, became fully attached to him once the two gods were merged, since a Roman audience already linked Neptune with chariot racing before the identification was complete.