Tusk and bone hut sites out of Mammoth bone made by
prehistoric humans, usually attributed to Cro-Magnons, during the Paleolithic period has been found (as deep as 22.5 m deep) in Czech Republic, Moravia, Poland and along the Dniepr river valley of Ukraine in Europe.
They may be the earliest structures built by prehistoric man, and thus the earliest examples of architecture, as evidence of increased social complexity and status differentiation during the final phase of the Ice Age.” (Paul G. Bahn (ed) 100 Great Archaeological Discoveries  54-55)
The huts and houses were circular or oval huts and as much as 15 to 20 feet in diameter.
The oldest are dated to be 27,500 years old, (Ukraine houses are dated at between 12,000 and 19,000 years ago) and whole villages have been found, being the oldest towns found. Humankind started creating urban centers like those clusters of homes 15,000 years ago, during the Ice Age.
Some of the most notable of these mammoth bone huts were found in Mezhyrich, a village in central Ukraine, where in 1965, a farmer dug up the lower jawbone of a mammoth while in the process of expanding his cellar. Further excavations revealed the presence of 4 prehistoric huts, made up of a total of 149 mammoth bones. Other interesting objects have also been found on the site, including a map inscribed onto a bone, presumably showing the area around the settlement.