Short answers, pulled from the story.
The cannon most likely originated in China, with the earliest known depiction appearing in a sculpture at the Dazu Rock Carvings in Sichuan dated to 1128. The earliest confirmed extant cannon is the Xanadu Gun, which bears an inscription dating it to 1298. Scholars generally agree the gun was born sometime during the 13th century.
The oldest extant cannon in Europe is a small bronze example unearthed in Loshult, Scania in southern Sweden, dating from the early-to-mid 14th century. It is currently held in the Swedish History Museum in Stockholm.
Sixty-eight Hungarian-made cannon bombarded Constantinople for fifty-five days in 1453, breaching walls that had been considered the strongest in Europe. The largest cannon, the Great Turkish Bombard, required 200 men, 70 oxen to operate, and 10,000 men to transport. The city fell on the 29th of May 1453, ending the Roman Empire's last remnant.
On the 13th of Vendémiaire 1795, Napoleon ordered cannon to fire grapeshot into a royalist mob of over 25,000 men attacking Paris, an event known as the "whiff of grapeshot". The attack ended the royalist threat and made Napoleon a famous public figure. He later massed cannon into batteries at engagements such as the Battle of Friedland, where 66 guns fired 3,000 roundshot and 500 rounds of grapeshot.
Cannon derives from the Old Italian cannone, meaning "large tube", which came from the Latin canna and ultimately from the Greek kanna, meaning "reed". The word has been used to refer to a gun since 1326 in Italy and 1418 in England.
Autocannons automatically fire a series of projectiles at a high rate, similarly to a machine gun, but use larger calibre explosive shells, typically 20 mm or greater. The typical rate of fire for a modern autocannon ranges from 90 to 1,800 rounds per minute, and rotary autocannons such as the GSh-6-23 can exceed 10,000 rounds per minute. Unlike machine guns, autocannons can fire explosive shells, making them more effective against armoured targets.