The Origin of Vampire Rules
Something I always find very funny in vampire media is, that vampires usually have those certain rules, right? Vampires usually cannot go out into the sun. Often they will not be able to touch crosses or even be paralyzed by just looking at a cross. They might be shapeshifters. Vampires often cannot cross flowing water, and they also cannot cross a home without an invitation. Sometimes they are weirdly allergic against garlic. Also sometimes they have no mirror reflection. Or even not a shadow. They might not be able to cross onto sacred land (so for example they cannot set food on church ground). And of course they need to drink an undefined amount of blood.
And yes, this is just another excuse to talk about some more mythology - and how stuff happened to end up culture the way it did.
Origins of the Vampire Myths
Chances are, that someone told you that vampires are literally everywhere in the world and one of those myths that somehow is everywhere around.
This is not true - and mostly goes back to people applying "vampire" to pretty much everything that is arguably undead. Even though most of those figures technically are arguably a lot closer to zombies. If it does not leech energy or blood from living people, it is not a vampire.
So, actually vampires were a very specific thing that originated specifically in Eastern Europe. We are fairly certain that the origin of the myth came actually from some Ancient Greek myth that spread out into those places and then shifted. But the vampire itself comes from Slavic Myths. In those we have a variety of beings, that would qualify as vampires. Strigoi, Upir, Lugat, Moroi and quite a lot of others. There was a lot of overlap between those creatures and "evil witches" in a lot of times, and not all of them actually drank blood, but they drained at least your energy in some way.
Among people studying folklore folks are fairly certain that the myths came originally from people not fully understanding certain sicknesses. So basically, when a village was struck by a sickness like that, people would go: "Oh, this has to have been Alfred coming back from the dead," because Alfred recently died and it was the best explanation they came up with. And because people did not understand how dead bodies worked, they also would then see stuff like the hair and nails appearing longer when they opened the grave, which they saw as a proof that the dead was not really dead.
Generally speaking, there were then a couple of things that would be done to prevent them from coming back. Some people would just behead the dead body, others drove a stake through the heart of the people, while others might just tie up the legs of the dead.
But yeah, the one thing is that vampires come mainly from Slavic cultures. This is the important bit about vampires you need to remember. Because a lot of this comes back to this.
The Vampire Rules are really fun, because they come together from three very different sources: From the fact that they were Slavic, from English folklore, and then from limitations in media.
So, let me go through typical vampire rules.
Vampires shapeshift: Vampires being shapeshifters goes back to Slavic mythology. In those vampires, witches and shapeshifters often were just the same kind of thing and had a lot of overlap.
Vampires cannot cross water: This originated probably in the Rennaissance. And it mainly originated from the fact that the people noticed that vampires only seemed to exist in Eastern Europe. Which people started to find weird. So, they had to come up with an explanation. And that explanation was: For some reason the vampires could not cross the Danube. This over time merged into "vampires cannot cross water".
Vampires are allergic against garlic: This is definitely something that goes back to the original myths. It is believed that this might be connected to the fact that garlic has an antibiotic effect. And as I said, vampire myths probably originated with unexplained sicknesses. So it is not hard to believe that people who ate garlic might not have gotten (as) sick, so folks were like: "Oh, the garlic kept the vampire away."
The stake through the heart kills vampires: This myth also comes from the vampire practices back then. On e way of burying a vampire in a way that it would not come back was to put a stake through the dead body.
The cross, not entering homes, and holy ground: Ironically, all those things that are probably connected to the same thing. Because these weaknesses are usually connected to more English folklore. While people definitely have hidden in churches (partly because of the law of sanctuary) forever, there is some good evidence that this actually comes more from British fairy culture - that then got applied to all other forms of paranormal creatures. And we know that around the 18th century, there was a whole big vampire scare in England, that definitely mixed a lot of Eastern European vampire lore with the lore of the Otherworld and Fae from Celtic mythology. Vampires having glamour of sorts probably is also connected to this.
Vampires do not have a reflection: This specifically is dated back to Bram Stoker, meaning everyone else after this just used this from Bram Stoker. The theory is that Stoker's idea was that mirrors somehow reflect the soul - something like that.
The Baptism of Blood: Another vampire thing that goes back to Stoker specifically is vampires having to exchange blood with someone to make them a vampire. Aka, drinking thier victims blood and then giving blood to them. In fact, in Stoker's work it was implied to have to happen three times until someone is turned a vampire. Which at least makes sure there are no accidental vampires.
Vampires drinking blood: Ironically the specific thing of vampires drinking blood also comes from Victorian Gothic literature. While this was not fully unheard off in mythology, it was not such a common trait there. But in Victorian literature it became THE vampire calling card. And this for two reasons. Reason 1: Welp, blood drinking is a neat symbolism for sex at time where you were not allowed to write about sex. Reason 2: ... Anti-Semitism and blood libel. I am sorry I could talk around this, but yeah, we definitely are certain that some of the Victorian vampires drink blood because the folks writing were implying blood libel. Welp.
Why Vampires Burn in the Sunlight: The dumbest bit of vampire lore I know is why vampires burn in sunlight. No, this does not originate with mythology - neither Slavic, nor Celtic. No, this does not go back to Dracula or another book of the time. Vampires in Victorian literature were fine and dandy in the sun. They might not be able to use certain magics, but other than that they were fine. No, the reason vampires burn in sunlight is... that the original Nosfertu ran out of budget, and needed a convenient way to dispatch the vampire. So they decided: "Oh, actually he burns in sunlight." And then, that stuck.