The Sedlec ossuary of Kutna Hora
Logical solutions can look disturbing in retrospect. Take a small area with a large population. Arable land has to be kept clear for farming, so the living can eat. There is not enough fuel to burn the corpses, but just enough to cook. Therefore, the buried dead are exhumed after a year of allowing the flesh to return to the soil. The place where they lay is used for another. Or more than one, because room is at a premium.
And, sometimes, the well-turned and enriched soil is swapped for poorer soil because nothing can be wasted.
There is nowhere to leave the bones. The living recognise the dead as important. They can not be disposed of like garbage.
But there is a need for building materials... And there has been a great deal of time devoted to fitting bones together in different ways. With a little bit of mortar, and some other chemicals to preserve the structure, it is possible to make housing out of the dead.
But humans didn't leave it there. They got...decorative. Rib chandeliers, scapula sconces, phalange features... it went on and on.
All the buildings had been left, along with several thousand artefacts, when the humans who had lived there had evacuated to escape some disaster that had long since passed. Wherever they had gone, they did not want to go back to a place where they had to make buildings out of the dead. Dust had settled on everything. Weeds had begun to encroach the infrastructure.
T'kelis crept silently through the buildings. Documenting everything. Trying to calculate how many had lived and died to dictate the construction of buildings or extensions like this. And, of course, paused at the ones that were too small to be adults. Those seemed to be universally placed in some kind of shrine. Articulated in a position of repose, or wrapped in pseudo-swaddling and always, no matter what, surrounded with dried flowers.
They felt the loss of their young more harshly than they felt the loss of an adult.
For all of the chaos implied by the things left behind, there were signs that they had planned the evacuation. Things left behind were left in ordered stacks. Food that would spoil was routinely left outdoors. Little remained of it bar the occasional container or remnant too tough for the local wildlife to ingest. And there were no colonies caused by abandoning pets to their fate.
And - unfortunately for T'kelis and her advisors - no hint of where they had gone. They had taken all their maps with them. None had been left with convenient marks to show their proposed destination.
The crops left in the fields had either died or gone feral, reverting to a gene set far more primitive and robust than their civilised or tamed counterparts. And it wasn't as if the Kresshki could use them.
"Anything?" said the mission commander K'tol.
"Negative," said T'kelis. "Signs of an orderly departure. No sign of where. It's a big planet. There's a chance we would never find them. There is a chance that they might find us."
"Noted. We'll mark this location as 'do not disturb'. If there's one thing people have in common, it's respect for the dead."
And they might look favourably on a people that respected their dead. Even if they were used to make buildings. When your people are stuck on a planet with humans, it's always for the best to try to play nice with them.
"Acknowledged," said T'kelis. She left a fresh flower on the bone altar that was at her last point of investigation. "Returning to the scout craft."