To purify the water from a certain river the monks have carved a section of the river that goes over a stone bed. Through holy carvings of gods, godesses, and holy symbols and then the river flowing over them, it purifies the water making it safe for drinking and/or makes it holy water. For rivers that do not have natural rock bottoms, large smooth stones can be carved and added to the water to fully cover the bottom.
The Chinese, when attacking a castle or fort, flew kites over the city wall and used the length of string it took to get it there as a measurement to know how far they had to dig a tunnel to get under the wall.
Silk Armor? The Mongols wore silk undergarments under layers of leather armor. Why? Because silk is very strong. If an arrow hit them and made it through their armor, it would usually not have enough energy to puncture the silk. It could still enter their body but, because the silk would not break, the arrow's barbs could not do their work and the arrow could easily be removed leaving a relatively clean wound considering normal arrow wounds.
A new substance is found in an out of the way area and kept very quiet. It is found to make a perfect counterfeit diamond. Only the most expert of expert appraisers would even have a hope of noticing that it is fake. Only one problem: if it gets wet it starts to slime and if it is saturated, it turns into a glob of gel.
A tree was given as a gift at one time to a city. Every year the tree is the center of a large parade as the tree is towed by oxen or large horses in a large wagon through town.
Village has a nearby natural substance that comes from the ground and burns well when lit. They use it only locally and try not to let the secret get out.
The nations of the Kolm surpasses all other barbarians in their wilderness of life. Thoug they do just bear the likeness of men, of a very ugly pattern, they are so little advanced in civilization that they make no use of fire, nor any kind of relish, in the preparation of their food, but feed upon the roots which they find in the fields, and the half-raw flesh of any sort of animal. I say half-raw, because they give it a kind of cooking by placing it between their own thighs and the back of their horses. They fight in no regular order of battle but by being extremely swift and sudden in their movements, they disperse, and hen rapidly come toghether in loose array. They spread havoc over the vast plains and flying over the ramparts, they pillage the camp of their enemy almost before he has become aware of their approach. They are the most terrible warriors for when in close combat with swords and flails they fight without regard to their own safety, and while their enemy is intent upon parrying the thrust of the swords, they will entangle him with their chains so that he loses all power of walking or riding.
Excerpt from "The peoples of the world" By Taklamarian court-scholar Guliman Amon.