Every single culture in the world shares a fear of the undead. Tales and wards against vampiric revenants have been found in civilizations ranging from medieval Romania to ancient China. Most share a few key traits. They were once human. They drink blood and eat flesh. They are neither alive nor dead. Like the creatures themselves, these myths sustain themselves by preying on people and their fears.
And, like most universal cultural touchstones, there are both real reasons why they exist and evidence left behind by those who believed in them. Partly the fear of undead may have arisen from ignorance of how a body decomposes. The classic signs, such as bloating, darkened skin, blood welling from the mouth, and even the lengthening of teeth and nails can be explained as atypical but not uncommon processes of death. The evolution of gases can even cause a corpse to groan. All you need after that is some relevant folk belief about wandering souls or evil spirits and, bam, you’ve got yourself a revenant.
And not only did older cultures believe in these spirits, some even took drastic steps to avoid them. Two bodies were recently discovered near Kilteasheen, Ireland, interred with giant rocks shoved into their mouths. One was so rudely interrupted that the jaw dislocated. The bodies are about 1400 years old, likely community outcasts or possibly plague victims. Similarly, in Lesbos, Greece, a skeleton was found literally nailed in his grave with iron spikes. This case, however, was much more recent; the man died sometime in the 18th century.
The first part of a documentary focused on the Kilteasheen graves can be found here on Youtube. More on this kind of history can be found at poweredbyosteons.org.