<p>St. Mark’s traditional athletic rival is the younger Groton School. St. Mark’s high school football rivalry since 1886 with Groton School is one of the oldest athletic rivalries in the United States, following the Andover-Exeter rivalry. The two schools have met in regularly scheduled athletic contests for more than a century. (See the List of high school football rivalries for more information.) St. Mark’s traditionally has a “Groton Day” celebrating this rivalry, just as Groton has a “St. Mark’s Day” with the same sorts of festivities.</p>