The Neptunalia is celebrated a.d. X Kal Sext. ‡ as a festival of Neptunus. Very little is known about the celebrations that took place on this day, or about the cult which would have celebrated it. About the celebrations of the day, Fowler 
says that huts or booths of foliage were set up by the cultores, but this only to protect those who came to worship Neptunus on that day.
Its placement in mid-Summer suggests also the connection with trade, particularly trade by sea, from an astronomical view. In light of the fact that the Moon is at its farthest distance from Earth at this time, waves would have been significantly less than at other times of the year, which would be favourable to any sea-based trade. This would have been an optimal time to propitiate Neptunus in the hopes that he would continue to keep the waves minimised, allowing easier and more successful trade.
This also connects to agriculture. This festival is placed in enough time before the harvest to allow cultores to attempt to propitiate Neptunus such that, when the time comes, farmers will be able to harvest their crops successfully and use them at the markets to trade and barter. The favour of Neptunus would be essential to allow goods from other parts of the Mediterranean to reach Rome and all of Italy safely, something which the agricultural community of early Italy would have desired more than not.
Modern Neptunalia Events in Nova Roma
- ↑ Fowler, W. W. The Roman Festivals of the Period of the Republic: An introduction to the study of the religion of the Romans (ISBN 1402148577)