is broadly defined as the area that is home to the Mesoamerican civilization, which comprises a group of peoples with close cultural and historical ties. The exact geographic extent of Mesoamerica has varied through time, as the civilization extended North and South from its heartland in southern Mexico. The term was first used by the German ethnologist Paul Kirchhoff, who noted that similarities existed among the various pre-Columbian cultures within the region that included southern Mexico, Guatemala, Belize, El Salvador, western Honduras, and the Pacific lowlands of Nicaragua and northwestern Costa Rica. In the tradition of cultural history, the prevalent archaeological theory of the early to middle 20th century, Kirchhoff defined this zone as a cultural area based on a suite of interrelated cultural similarities brought about by millennia of inter- and intra-regional interaction (i.e., diffusion). Mesoamerica is recognized as a near-prototypical cultural area. This term is now fully integrated in the standard terminology of pre-Columbian anthropological studies. Conversely, the sister terms Aridoamerica and Oasisamerica, which refer to northern Mexico and the western United States, respectively, have not entered into widespread usage. Some of the significant cultural traits defining the Mesoamerican cultural tradition are: Horticulture and plant use: sedentism based on maize agriculture; floating gardens; use of bark paper and agave (see also maguey) for ritual purposes, as a medium for writing, and the use of agave for cooking and clothing; cultivation of cacao; grinding of corn softened with ashes or lime; harpoon-shaped digging stick Clothing and personal articles: lip plugs, mirrors of polished stone, turbans, sandals with heels, textiles adorned with rabbit hair Architecture: construction of stepped pyramids; stucco floors; ball courts with stone rings (see the use of natural rubber and the practice of the ritual Mesoamerican ballgame) Record keeping: use of two different calendars (a 260-day ritual calendar and a 365-day calendar based on the solar year); use of locally developed pictographic and hieroglyphic (logo-syllabic) writing systems; numbers (see also vigesimal (base 20) number system); "century" of fifty-two years; eighteen-month calendar; screen-fold books Commerce: specialized markets, "department store" markets subdivided according to specialty Weapons and warfare: wooden swords with stone chips set into the edges (see macuahuitl), military orders (eagle knights and jaguar knights), clay pellets for blowguns, cotton-pad armor, traveling merchants who act as spies, wars for the purpose of securing sacrificial victims Ritual and myth: practice of various forms of ritual sacrifice, including human sacrifice