Population Migration / Travel
The vampires were running out of healthy blood. So they started sucking everything they could from the healthy. They grabbed a few humans and fleed to the mountains.
It got harder to find any healthy blood in Tamjian, and the vampires were getting desprate. They needed food soon, or they might die. And as they thought that, they also knew death could not be avoided. Either they would die, or someone else. So they kidnapped a bunch of humans. (There were a bunch of them, and they were less sick.) They sucked a couple of them dry, and then the little group along with their newly aqired humans. They fleed to the mountains. It took some time to get all 500 vampires housed, not to mention the humans, but they made some sturdy homes. They can still be seen today. Now they are used as check points by mountain climbers and as tourist spots. They were last renovated in 2000.