Caligula ordered his troops to collect seashells. He claimed he conquered the Ocean and those were the spoils of war!

de bene esse: literally, of well-being, morally acceptable but subject to future validation or exception

There are few surviving sources on Caligula's reign, although he is described as a noble and moderate ruler during the first two years of his rule. After this, sources focus on his cruelty, extravagance, and sexual perversity, presenting him as an insane tyrant.
While the reliability of these sources has increasingly been called into question, it is known that during his brief reign, Caligula worked to increase the unconstrained personal power of the emperor. One of his outlandish expeditions was to the English Channel, where he ordered his troops to collect seashells. He took them back to Rome claiming they were the spoils of war and that he had conquered the ocean.

He directed much of his attention to ambitious construction projects and notoriously luxurious dwellings for himself. However, he initiated the construction of two new aqueducts in Rome: The Aqua Claudia and the Anio Novus. During his reign, the Empire annexed the Kingdom of Mauretania and made it into a province. In early 41 AD, Caligula became the first Roman emperor to be assassinated.