Neptune is the Roman form of Poseidon. As Neptune, he becomes more disciplined, militaristic, and warlike than his Greek counterpart. For Greeks, he was a major civic god and was highly respected for being the god of the sea and earthquakes. However the Romans, who were not seafaring people, associated him more with fresh water and horses, and treated him with a fearful respect.
The Romans believed in a series of gods associated with world around them. They designated Neptune as the god of water and the sea, a close parallel to the Greek god, Poseidon.
As a god of both fresh water and the sea, Romans prayed to Neptune to provide water for their crops. In ancient Italy, farmers would honor Neptune with a festival in July, when frequent droughts would destroy their fields. He was also a patron of horses and had a temple called Circus Flaminius built near a race track, and another in Campus Martius.
He was also the patron of horse racing and a temple dedicated to him was situated near the Circus Flaminius which was a Roman racetrack. The Circus Flaminius was the venue for horse racing with one rider and his horse going around the turning posts. In the famous story of the Aeneid, Neptune was resentful towards the Trojans, but is not as vindictive as Juno. He was so annoyed that Juno had intruded on his domain that he helped the Trojan fleet against the efforts of Juno who tried to wreck their ships.
Poseidon arrives wearing a hat saying: Neptune's lucky fishing hat.
He is highly feared at Camp Jupiter as well as by all Roman demigods in general, and his children are considered bad luck and dangerous to have around. Unlike most of the other major gods, he only has a shed as a temple on Temple Hill, with a cobweb covered trident nailed above the door, and three dried up, moldy apples left inside as an offering. Part of the reason Camp Jupiter considers his children bad luck is because of an event in 1906, when his descendant, Shen Lun, was thought to create a major earthquake and was banished from the camp. While Percy Jackson was at Camp Jupiter, he prayed to Neptune in his temple for some help.
While Jason Grace and Leo Valdez are trying to capture the dwarfs, Akmon and Passalos, at Bologna they see a statue of Neptune. Jason said that he would feel better if he saw a statue of any god other than Neptune. Later, the statue suddenly shoots some rope from its hand and ties up Jason. Luckily, he manages to escape.
- As one of the Big Three, Neptune has the ultimate powers a god can possess, and is rivaled only by his brothers, Jupiter and Pluto.
- Hydrokinesis: As the Lord of the Sea, Neptune has absolute control over water like Percy, only to a much greater extent.
- He can withstand any amount of water pressure.
- He can generate water from his body.
- He can use sea waves as a form of teleportation.
- He can breath underwater.
- He can communicate with sea creatures.
- Geokinesis: Being the god of earthquakes, Neptune has the ability to cause earthquakes, giving him the nickname "the Earthshaker".
- Atmokinesis: As the god of Storms, he has absolute control over the weather.
- Aerokinesis: Neptune is also known as the god of storms since he controls the weather over the seas. He can create thunderstorms and hurricanes. However, he can also create clear skies for sailors if he wants. As god of the seas, it is unknown how far this power may extend over land.
- Neptune is the eighth and farthest planet from the Sun in the Solar System. It was named after the god, as its deep blue gas clouds gave the earliest astronomers the impression of great oceans and seas, the domain of Neptune.
- Caligula, a Roman emperor, once declared war on Neptune's kingdom. Once he found he could not attack the sea, he had it whipped.