The Boston Marathon is always held on Patriots' Day, which is an annual holiday that falls on the third Monday in April. This is a civic holiday in Massachusetts and Maine that commemorates the Revolutionary War battles of Lexington and Concord, which took place in Massachusetts near Boston.
Though the Boston Marathon has become a particularly popular event starting in the late 1990s, this race has been run every year since 1897. Even in this early year, the marathon was held on Patriots' Day, which is a particularly important holiday in the Boston area. The weather in Boston is always variable in April and may be wintery or spring-like, depending on the year.