Opened to the public on this day in 315 and spanning Rome’s Via Triumphalis amid the decennalia, a series of festivities and games held every decade since 27 BC when Augustus declined the offer of supreme power for life but would accept it for a decade—a tradition upheld by later, non-term-limited emperors to solemnise (they would symbolically relinquish imperium only to have it foisted back on them by popular acclaim) the sacrifice of their predecessor, the Arch of Constantine was dedicated by the Senate to celebrate the the tenth year of his reign and his victory over the forces of Maxentius during the Battle of the Milvian Bridge, ending the civil wars of the terarchy, power disputes among the co-emperors. 
The decorations and the frieze, recounting Constantine’s exploits, along the crowning entablature and colossal proportions make the fourth century archway one of the most iconic examples of the architecture of late Antiquity, but there is some scholarly controversy on its actual builder and purpose, some suggesting it was the vanquished Maxentius who began its construction, his imprimatur erased by damnatio memoriae, particularly since as the emperor was by then more interested in founding his new capital in the East, Constantinople, rather than erecting public buildings in a declining Rome.
synchronoptica
one year ago: assorted links worth revisiting (with synchronoptica)
seven years ago: the French comic that heavily influenced Star Wars, domestic double-agents plus the heart of man
eight years ago: alchemist Paracelsus plus the châteaux of the Loire
nine years ago: more links to enjoy
eleven years ago: a mystery ranging leaflet