July 23rd was the day the ancient Romans celebrated Neptunalia – a two-day festival in honour of Neptune as god of waters, celebrated at Rome in the heat and drought of summer. The idea was to appease Neptune so he would send rains to keep the crops healthy. The people used to build huts of branches and foliage in which they probably feasted, drank, and then slept overnight, continuing the fun the next day.
In ancient calendars these days were marked as Neptune ludi et feriae. Ludi means games and Feriae festival or feast. This implies that the celebrations consisted of games and sports as well as feasting. Neptune is sometimes associated with horses so it seems likely that horse racing was the order of the day, indeed his temple in Rome was close to the Circus Flaminius – the horse racing statidum