Some 500 years ago Europe was inundated with swarms of flies during the summer months. This combined with memories of the plague called for some sort of action by citizens.
By the 1500s folks in Germany had figured out that the plague had taken fewer victims in areas that adhered to certain hygienic standards. Cleanliness made a difference in who lived and who died so laws were passed to encourage citizens to leave their filthy ways to the past. One of those laws was that all food and beverage containers had to have lids to protect people from dirty insects.
Covered containers were just a small part of the movement to clean up the community. Another law required that beer could only be made from hops, cereals, yeast and water. This allowed for a better quality beer and did away with the recipes that made beer from rotten bread and such.
Long story short is that the beer industry took off in Germany and has never looked back. The covered beer stein was one innovation that took the fancy of the population long after the threat of disease had passed. The upper class would have had their beer steins made from pewter but the commoner would have embraced those made of pottery. Other mediums used would have included ivory, porcelain, wood, silver and more. Everyone would have had their own individual stein and some of them could be right fancy. All sorts of designs from coats of arms to biblical scenes have turned up on the outside of these steins.
When the industrial age hit beer steins became less expensive to make. Instead of individually molding pottery into a mug they could now be mass produced with each design having a sharpness once associated with the hand made. Strong pottery seemed to be the chosen medium for most steins however glass and pewter did enter the market in a big way.
Finding one of these beauties would be a treat for the collector. Over a 500 year period there would have been lots of steins made in Germany for the discerning collector to find. For the collector of the original steins they can expect to pay hundreds of dollars. Those who collect steins issued by American breweries will pay considerably less.