Barrio Histórico, south of the government and convention centers, is a remnant of the old Mexican barrio that once lay outside the presidio walls. (Barrio Libre, or free zone, is a name for one portion of the district.) Classic Sonoran adobe row houses, in a rainbow of colors, front the streets. Dating from the mid to late 1800s, the houses also include transformed Sonorans and red-brick Queen Annes. About 225 contributing properties enliven 20 blocks, where new construction is also underway.