valuable piss

throughout European history the amount of piss being collected has strong correlation with the prosperity and strength of the society.
In Ancient rome, Piss (usually human) was the only source of ammonia which was used as:
1. Bleach to keep the clothes white
2. Toothpaste to keep the tooth white.
Richer the city, the more piss was collected/transported to the city so that the rich could afford these luxuries. BTW till about a 100 years ago, ammonia was the key active ingredient in almost all the toothpastes.
In the medieval ages, gun powder was the symbol of power and wealth. More the number of guns were shot, the more blackpowder was needed. One of the most important component of blackpowder was saltpeter which was almost exclusively made from Piss (but animal piss this time). http://www.musketeer.ch/blackpowder/saltpeter.html
In the modern era, there were cheaper ways to produce ammonia and nitrous oxides, but that never diminished the importance of these compounds. Ammonia is used even today in Urea and almost all fertilizers, while nitrous oxides are still the most important ingredient of all explosives, bullets and weapons. Its even said that the Allied bombing lead to destruction of several important sites that produced Nitrous oxide. This severely reduced the supply of nitrogen for Hitler and almost all was being diverted to make explosives. This caused a famine which started a chain of events leading to invasion of Russia (for its fertile land and supply of Potato and wheat)