Imagine a long, long time ago in a big city called Rome. The people there liked to do something special every October called the "October horse". They picked the best horse they could find and decorated it with pretty flowers and ribbons. Then, they had a big parade where they all cheered and celebrated the special horse.
But there was a catch - after the parade, they would pick a special man who was very brave and strong, called the Flamen Martialis, to ride on the special horse. They would have a big race where the Flamen Martialis would try to ride the horse as fast as he could through the city.
Now, the people of Rome believed that the horse represented the crops and the earth's fertility, and that the race would bring good luck and prosperity for their city. After the race was over, they would sacrifice the special horse, believing that its blood would bring even more good luck to their city.
So for the people of Rome, the October horse was a really big deal. They celebrated it every year to bring good luck and prosperity to their city.