Neptunalia
According to Varro, Neptunalia was celebrated on 23 July, one of the dies comitiales, when committees of Roman citizens could vote on civil or criminal matters. It may well have been tiresome for those called out on jury duty, knowing that other wealthy Romans were meanwhile enjoying a delightful picnic in the shade of bay leaf arbours.
For Neptunalia was a summer festival, and a time to return to Nature.
Neptune himself was an indigenous deity of the waters and had, by the time these happy Roman picnics were taking place, been largely replaced by Poseidon, the powerful Greek Olympian and God of the Sea. (See more on Poseidon, God of the Sea.)