The name of today's festival is derived from "horse," of course! And horses are what the main event of today includes (or would include, if we were ancient Romans). As the whole of February was also dedicated to Mars, this is a Mars festival day: horse races on the Campus Martius!

And also HAPPY BIRTHDAY CALPURNALIA! BENE FECIT! MANY A YEAR!

*huge, red, underlined grin*