It's basically all about evil spirits, people
Wedding announcements were traditionally issued in order to prevent incest
The Roman Catholic tradition of 'posting banns' dates back to the early 13th century and was introduced in order to give people the chance to denounce unions as clandestine or incestuous.
Grooms used to kidnap their brides
The 'kidnapping the bride' tradition first appeared thousands of years ago when Romulus, founder of Rome, invited residents of Sabine to a party and then abducted all the female guests. (As you do.) The tradition was perfectly normal in England up until the introduction of the Marriage Act in 1753. However, it still takes place with disturbing regularity around the world.
The Best Man
The usher who proved himself to be the most useful was appointed Best Man. He was the 'best' owing to his loyalty to the groom, as well as his fighting skills and kidnapping abilities.
The bride stands to the groom's left at the altar because...
Traditionally speaking, he needed his right hand to be kept free in order to fight off other potential kidnappers. Obvs. That's also why the Best Man stands at the top of the aisle - so he can help the groom deal with any potential interlopers.
The wedding party
Way-back-when, bridesmaids would wear identical outfits to the bride, meaning a potential kidnapper would be thrown.
The 'giving away' of the bride
The idea of a bride's father 'giving her away' isn't quite the sweet, symbolic moment you might think - originally, it represented the transfer of the bride, as her father's property, to her groom.
The wedding veil
Stemming from the Ancient Greeks and Romans the wedding veil was incorporated into the bride's outfit in order to - you guessed it - ward off evil spirits. Whilst the Greeks wore yellow veils, the Romans opted for punchy shades of red, with both intended to represent fire.
The wedding bouquet
The wedding bouquet wasn't always about pretty flowers. The Ancient Greeks would hold handfuls of herbs to ward off evil spirits.
The bouquet throw
Hence the birth of the bouquet-toss tradition, in a bid to stop the attack.
Carrying the bride over the threshhold
Carrying the bride over the threshhold wasn't always a super-sweet, romantic moment - rather, it was more of a practicality thing. Living in fear of evil spirits, Roman grooms would lift their bride over the threshhold to protect them from devilish demons who were believed to live in the floor.
After swapping their vows, Ancient Norse couples would go into hiding for 30 days. During this time, they would be brought supplies of honeyed wine - hence the concept of the 'honeymoon' came into circulation.