In the Southwestern United States, Pueblo (capitalized) refers to the Native tribes of Puebloans having fixed-location communities with permanent buildings which also are called pueblos (lowercased). The Spanish explorers of northern New Spain used the term pueblo to refer to permanent indigenous towns they found in the region, mainly in New Mexico and parts of Arizona, in the former province of Nuevo México. This term continued to be used to describe the communities housed in apartment structures built of stone, adobe mud, and other local material. The structures were usually multi-storied buildings surrounding an open plaza, with rooms accessible only through ladders raised/lowered by the inhabitants, thus protecting them from break-ins and unwanted guests. Larger pueblos were occupied by hundreds to thousands of Puebloan people. Various federally recognized tribes have traditionally resided in pueblos of such design. Later Pueblo Deco and modern Pueblo Revival architecture, which mixes elements of traditional Pueblo and Hispano design, has continued to be a popular architectural style in New Mexico. The term is now part of the proper name of some historical sites, such as Acoma Pueblo.