The Pope tells his sons that in all of history, Rome had only been sacked twice. In fact, up to that point in time, Rome had been sacked 5 times (or 4 times since the papacy was established): by the Gauls in 390 BC, the Visigoths in 410 AD, the Vandals in 455 AD, the Ostrogoths in 546 AD and the Normans in 1084 AD.
The use of chain-shot first occurred in 1631. Although Charles VIII revolutionized several aspects of artillery this was not one of them.
Juan refers to the college of cardinals as lemmings when they flee the Vatican in anticipation of an impending French invasion. He's several centuries too early to use this expression. The popular myth of mass lemming suicide began when the Walt Disney movie, 'Wild Wilderness' was released in 1958. Furthermore, lemmings only live in the Arctic tundra and would be unheard of in 15th century Italy.