Cue the housemade tortillas and salted margarita rims, we're celebrating Cinco de Mayo in Seattle. And right off the bat we will clear the misconception that the day commemorates Mexico's independence that would be in September. Cinco de Mayo, the fifth of May, is an annual celebration observed to commemorate the Mexican Army's victory over the French Empire at the Battle of Puebla, on May 5, 1862. The victory of the smaller Mexican force.