Not to be confused with the Gospel author of the same name, Mark was a Roman by birth, according to the Liber Pontificalis. He appears to have been a priest or deacon under Pope Miltiades (two popes ago) when Constantine asked for a group of bishops to deal with the Donatist heresy. He oversaw the building of two churches during his short tenure as pope, one of which is now known as the Church of San Marco (St. Mark) inside the walls of Rome. The other was built over the Catacomb of Balbina outside the city, the same cemetery where Pope St. Mark would eventually be buried. He reigned for less than a calendar year, being elected on January 18 and dying on October 7, his feast day.

St. Mark is known for having given instruction on how subsequent popes were to be installed into office. The Liber Pontificalis attributes two documents to this pope, one of which states that the Bishop of Ostia (a diocese on the west coast of Italy) was given a pallium by St. Mark, as well as the responsibility of consecrating the newly-elected Bishop of Rome. Though the document itself doesn’t exist, it’s reasonable to accept this as fact given that St. Augustine recognized the practice by the end of the same century.

Fun fact: Despite only being in office for nine months, St. Mark doesn’t even crack the top 10 for shortest papacy!

During St. Mark's papacy, Arius, the perpetrator of one of the most widespread heresies the Church has ever seen (see yesterday’s pope), collapsed and died in the street in Constantinople, at the ripe old age of 80. Unfortunately, the heresy didn’t die with him, and continued to scourge the Church for decades.