The trident of Poseidon and its Roman equivalent, Neptune, was their traditional divine distinguishing mark that appears in many artistic representations from the ancient period. According to Hesiod's account, Poseidon's trident was made by the three Cyclops.
According to Robert Graves, however, both Poseidon's trident and Zeus's lightning bolt were originally sacred labrys, but were later distinguished from each other when Poseidon became the god of the sea and Zeus claimed the right to be master of the lightning bolt.
According to another view shared by Friedrich Wieseler, E. M. W. Tillyard and several other scholars, Poseidon's trident is a fish-catching spear used by the Greeks on the seashore. In this sense, it resembles the sharp-toothed pitchfork used by Mediterranean fishermen to catch eels.
Poseidon became particularly revered in coastal countries, where fish was a staple commodity. According to a competing idea by H. B. Walters, Poseidon's trident has a similar role to Zeus' sceptre, as Poseidon is the marine equivalent of Zeus.
In Greek mythology, Poseidon uses his trident on numerous occasions. During the confrontation with Athens over possession of Attica, Poseidon strikes the Acropolis with his trident to create a spring of sea water In a similar myth Poseidon strikes the earth with his trident to create a horse for mankind, while his rival, Athens, creates an olive tree.
The earliest coins made in Poseidonia in the 6th century BC contain depictions of the trident held by Poseidon in his right hand, similar to Zeus' thunderbolt. A red kylix from Attica dating from around 475 BC contains a depiction of Poseidon killing the giant Polybotes with his trident.
In another myth, Poseidon creates a spring or springs after striking the earth with his trident to reward Amimona for coming to meet him. In another version of another myth Poseidon wields the trident to scare off a satyr who was trying to rape Amimona after she accidentally hit him with a hunting spear.
There is also a myth in which Poseidon touches the island of Delos with his trident, pinning it firmly to the seabed. Another myth recounts how Poseidon, enraged by the disrespectful behaviour of Aiax the Lesser, split with his trident the rock to which Aiax was clinging.
During a visit to Athens, the geographer Pausanias was shown in the Erechtheion the alleged imprint of Poseidon's trident on a rock and the fountain of seawater which he writes plays the sound of waves when the south wind blows.
The Roman scholar Maurus Servius Honoratus claimed that Neptune's trident had three teeth because "the sea is said to be the third part of the world or because there are three kinds of water: seas, rivers and streams." According to the second and third Vatican mythographers, Neptune's trident symbolizes the three properties of water: liquidity, fecundity and potability.