Perhaps no Roman Emperor has had such bad press as Caligula. There are many tales about his madness and cruelty, including one that claims he declared war on a Roman god. How true is it?
The Romans didn’t declare war on Neptune. However, a story says that Emperor Caligula ordered his soldiers to whip the ocean and pick up seashells as war spoils. If real, the story is likely a misunderstanding of what Caligula said or a sarcastic whim by him, but it wasn’t a real war.
The truth about Caligula is more complex than it seems at first. There’s not a single answer to what happened at the coast of the English Channel in 40 A.D., but historians had made some educated guesses.
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Who Was Neptune and Poseidon?
Neptune was the Roman version of the Greek god Poseidon. Poseidon was god and ruler of the sea, and he was among the most powerful gods in Olympus. The Romans adopted Greek gods and changed their names. Basically, Neptune and Poseidon are two names for the same god.
After defeating the Titans, Poseidon and his two brothers, Zeus and Hades, drew lots to distribute the ruling of the cosmos. 
Zeus ended up ruling over heaven and earth, Hades over the Underworld, and Poseidon over the ocean. This makes him second only to Zeus in power and authority.
Over time, the Greek pantheon of gods had a strong influence on Roman religion. There were Greek settlements in Italy long before the Empire existed, and the Romans eventually took over Greece and made it part of their Empire.
This constant contact with Greek culture caused the Romans to adopt many Greek gods, making slight modifications to better fit their culture. 
One of the Romans’ main changes to Greek gods was their names. Thus, Zeus became Jupiter, Hera became Juno, and Poseidon became Neptune.
Although Roman gods aren’t exactly the same as their Greek counterparts, most of their stories and overall characteristics were similar.
Many Greek literary hallmarks were translated to Latin, with the names of the gods changed to their Roman equivalents. Poseidon — or Neptune in Latin translations — is an important character in many of these stories, like the Odyssey and the Iliad.
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Why Do People Believe Caligula Declared War on Neptune?
People believe Caligula declared war on Neptune because of a possibly false or exaggerated story written about him by historian and Senator Seutonius. The story only states that he ordered his soldiers to pick up seashells, but it has been deformed over time.
When it comes to Caligula, it’s hard to discern fact from fiction. Most of what the world knows about him was written with some degree of hatefulness or vindictiveness.
The main sources for the life of Caligula are texts written by Roman Senators. It so happens that Caligula had an open struggle against Senators for power over the Empire.  He constantly badmouthed those who opposed him and perhaps publicly humiliated some of them.
Eventually, in the year 41, Roman Senators conspired with the army to have Caligula killed and take power from him.  Most stories about Caligula were written after that incident, sometimes centuries later.
The most popular account of his life comes from the Roman historian and Senator Seutonius. Another popular account comes from Seneca, who was also a Senator. Both men were interested in portraying Caligula in the most negative way possible.
It was a way of giving credibility to their version of their story and their grasp at power. And it wasn’t new or rare: the same happened with other emperors, like Nero.
In his biography of Caligula, Seutonius tells that after aborting his invasion of Britain, Caligula
“…drew up a line of battle on the shore of the Ocean, arranging his ballistas and other artillery; and when no one knew or could imagine what he was going to do, he suddenly bade them gather shells and fill their helmets and the folds of their gowns, calling them “spoils from the Ocean, due to the Capitol and Palatine.” 
Over time, this fragment deformed into the popular story of Caligula declaring war on Neptune, god of the sea.
Ancient historians ascribed this story and many others to Caligula’s madness. He supposedly made a bridge of boats across the Bay of Naples just so he could cross it in his chariot and planned to turn his horse into a Consul. He was sexually promiscuous, a rapist, and enjoyed cruelty.
Caligula enjoyed honoring himself in an extreme manner. He built two temples consecrated to himself in Rome. He even ordered the erection of a statue of himself in the Temple of Jerusalem.
However, modern historians put doubt in much of what was said of Caligula.  Some have speculated that he suffered from illnesses like epilepsy and insomnia. In any case, these stories were likely sensationalized and made to fit the fictional archetype of the tyrant.
Caligula was likely arrogant and egotistical, but the most outlandish stories about him, including his supposed war against Neptune, are probably exaggerated or made up.
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What Do Seashells Have To Do With the War on Neptune?
Seashells sit at the center of the story of Caligula and his supposed war against Neptune. Although it’s not clear what exactly happened, some records say that Caligula ordered his legions to collect seashells as spoils from the war against the sea.
Caligula set out to conquer Britain in an attempt to gain fame and respect. The invasion reached the people of Gaul, who were plundered relentlessly. However, soon after, the campaign was aborted. Likely, it was because the Roman army was reluctant to go through with it.
One theory says that, in an outburst of rage, Caligula gave the order to collect seashells as a way to humiliate his soldiers. Since they weren’t willing to cross the sea and reach Britain, Caligula might have found sarcasm in making them “go to war” with the sea and pick seashells as spoils.
It’s also possible that he ordered his legions to collect seashells to pass them as spoils of war and not return to Rome empty-handed. The whole campaign could have been a way of avoiding a mutiny against him.
Another theory states that seashells come to the story as a misunderstanding. Perhaps Caligula was referring to a military slang that used the Latin word for seashell to mean something else.
Thus, when Caligula talked about “picking up seashells,” he might not have said anything related to Neptune. Rather, it might be a reference to the military tents known as “seashells” or to the brothels his soldiers frequented —they might have used “seashell” as slang for vagina.
Many stories about Caligula are exaggerated or false. The claim that the Romans declared war on Neptune is almost certainly one of them.
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