Pueblos are modern and old communities of Native Americans in the Southwestern United States. The first Spanish explorers of the Southwest used this term to describe the communities housed in apartment-like structures built of stone, adobe mud, and other local material. These structures were usually multi-storied buildings surrounding an open plaza. The rooms were accessible only through ladders lowered by the inhabitants, thus protecting them from break-ins and unwanted guests. They were occupied by hundreds to thousands of Pueblo people in the larger ones. Several different federally recognized tribes have traditionally resided in pueblos of such design.