It's widely accepted that Emperor Constantine I had an insatiable thirst for gloating. So, when he defeated Emperor Maxentius and took the throne in 312, no one was surprised when he built this arch to commemorate his victory. Most of the artwork on the arch was plundered from existing monuments and modified to alter its meaning.
Some historians contend that the artisans of the 4th century simply didn't have the talent to create such ornate pieces, and only completed the arch by recycling old master works from ruins around the city. A preposterous claim, as the Romans never copied anything.
See what I did there? Sarcasm.