Bhutanese architecture remains distinctively traditional, employing rammed earth and wattle and daub construction methods, stone masonry, and intricate woodwork around windows and roofs. Traditional architecture uses no nails or iron bars in construction. Characteristic of the region is a type of castle fortress known as the dzong. Since ancient times, the dzongs have served as the religious and secular administrative centers for their respective districts. The University of Texas at El Paso in the United States has adopted Bhutanese architecture for its buildings on campus, as have the nearby Hilton Garden Inn and other buildings in the city of El Paso.