A custom, a prophecy, a lie, or there is simply a shortage of anything else... in short, in order for it to hold, you'll need to add some human blood or an entire human somewhere.
Can be a form of Sadistic Choice
. Also a form of Powered by a Forsaken Child
- Invoked in 300: a Persian emissary sees that the Spartans have stacked up the bodies of the Persian soldiers, and they tell him their blood served as mortar.
- In Dark Apostle, the Ghethsemenacht is a tower made of recycled Imperial buildings and glued together with human puree, built as a monument to the Chaos Gods. One of the slaves working on it discovers this when he finds a human tooth in the mortar.
- In The Left Hand of Darkness, an Earthman notices all the bridges in Karhide have keystones set with pinkish mortar. Turns out they believe an arch will fall without a bloodbond. They used to mix the mortar with human blood and bones, but these days, animal substitutes are used.
- An example from No Man of Woman Born: In the Merlin-1998 mini-series, Vortigern consults a soothsayer to find out why his castle keeps falling. The Soothsayer (taking false information from Mab) tells him to mix the blood of a man with no mortal father into his mortar and the castle will stand. Merlin, who was the only candidate found, knows that there's a spring under the castle, so he's basically building on water.
- In the Ravenloft D&D setting, the House of Lament became cursed when a former owner had a young woman buried alive in its foundation, ostensibly because it was required (but in truth because he was a sadistic creep).
- In God of War, the temple that contains Pandora's Box also contains the tombs of its architect and his family- apparently the gods required their sacrifice for the temple's construction. Some of the puzzles found within require the family members' skulls as keys.
- Eternal Darkness: The Pillar Of Flesh is constructed by The Ancients to facilitate their entry into our world. It is built of people smothered with concrete.
- In The Secret World, the headmaster of Innsmouth Academy refutes the rumor that the school has a skeleton in every closet, he proudly declares that the skeletons are bricked into the walls. The school installs the corpses of mages into the walls and foundations to bolster its magical defenses and the power they have to work with.
- "London Bridge" Build it up with blood and bone, blood and bone, blood and bone, build it up with blood and bone, my fair lady.
- Research has proven that blood really does make good mortar. Specifically, it makes cement stronger and lighter. (United States Patent 4203674).
- An old Chinese legend contains a variation. It tells about a bell which did not come out right during the casting. The ruler said the person making it will be killed if there will be one more failure. His daughter was foretold a young maiden's blood needs to be added. She jumped into the molten metal. It worked.
- There is a bunch of myths about The Great Wall Of China. Some says that both animal and human bones was mixed into the mortar, other says that the people who died building it got buried inside the wall and used as a filler.