St Mark was one of the four evangelists and the author of the second Gospel, "The Book of Mark", as well as one of Jesus Christ's 70 disciples or apostles, who were appointed by Jesus Himself and sent out in pairs on the mission to spread the gospel message (Gospel of Luke, 10:1–24). According to the Catholic tradition his feast day falls on April 25, the day of his death in year 68 AD. St Mark is regarded as one of the most important and beloved saints of the whole Christianity for his kinship to St Paul and St Peter and for being author of one of the Gospels.
The feast day is particularly honoured in Venice, of which St Mark is the patron saint, and where his relics have been resting for centuries inside the Basilica dedicated to him and located in Piazza San Marco, adjacent and connected to the Doge's Palace.
Image: "San Marcos", circa 1630, by Jusepe Leonardo (or José Leonardo, 1601-1653), a Spanish painter of the Baroque period.
Source: Jusepe Leonardo [Public domain or Public domain], via Wikimedia Commons