Summanus is the Roman god of nocturnal thunder – counterpoint to Jupiter’s daylight thunder. In Rome a temple was dedicated to Summanus sometime around 278BC, after lightning struck a statue of Summanus that stood on the temple of Jupiter one night.
The temple was formally dedicated on June 20th, and each year on that day wheel-shaped cakes made of flour, milk, and honey (called summanalia), were offered to Summanus. While these cakes may have been a solar symbol, two black oxen (or castrated rams) were also offered to Summanus, and black animals were usually offered to chthonic deities.
The origins of Summanus are not clear, but it is possible he may have originated with the Etruscans, if he was not even older than that. While he was once a popular god among the Romans, likely even more popular than Jupiter at one point, in later times much of his character was unknown even to them. The Roman poet Ovid once wrote "the temple is said to have been dedicated to Summanus, whoever he may be."