The building no. 1 in the Monumental Area is one of the largest excavated sections of Shahr-i Sokhta. Excavations of this building took place between 1999 and 2009. The building is sited in the square O with 250-meter dimensions on the northern side of Tepe.
Up to 1999, the likely defensive wall, tower, and public buildings of the site had not been excavated. That year, the expedition extended its investigations to the Great Monumental Area, bringing to light the remains of a large building, filled by different levels of debris, with thousands of pottery fragments and other cultural material. To date, about 1600 sq.m of this building have been excavated, revealing 90 different open spaces and rooms. The walls of this structure are solid and built with mud-bricks, while the height of the remaining walls of the central rooms reaches about 3.30 m. Two different staircases have been found in this building. One of them is made up of 8 steps of mud-bricks, 320 cm long, 40 cm. wide and 20 cm high.
Hundreds of anthropomorphic and zoomorphic clay figurines, seals, seal impressions, jar stoppers, disks, cloth, ropes, wooden and stone objects and pottery vessels have been found in various rooms of this last building. During the different phases of occupation of the site, this structure has been repaired and its plan and usage have been changed.
It contains six construction phases, five phases A-E of periods II and III, and the most recent phase i.e. phase F could be probably attributed to the last century of the period III and the first decades of period IV. Up to now an area of approximately1600 sq. m of this building has been excavated, and the results show that the function of this building may vary from being a distinguished structure such as a temple to a complex of small residential units.
As mentioned above, this building is large, with tens of rooms/ spaces and 6 structural levels (Levels A-F) of periods II and III. Level A is the oldest and most structures of this level are storage rooms, containing seals, seal impressions and other administrative objects. Level B is not well-documented, although changes are seen in the use of the architectural complex. Level C is somehow similar to the previous one. In Level D the Building becomes a large structure, perhaps attesting growing social complexity in Sistan. The main entrances are on the southern side, living spaces are on the central axis and storage spaces on the eastern and western margins. About 50 Spaces were excavated in Level E, but the main part of the structures of this level consists in 10 rooms. Level F is the last one, later on this part of the settlement was abandoned. Building 20 lies northwest of Building 1. Excavations lasted only 25 days and are not complete. The complex has 12 spaces disposed in a north-south direction with a coherent architecture of mud bricks. Rooms have right angles and walls approximately 70 - 80 cm thick. The main entrances of building were generally painted with two layers of red and white plaster. In spaces 4 and 5 were found two very large fireplaces, filled with a large amount of ash and charcoal. The exterior of the fireplaces were coated with white clay plaster. According to the very few materials, mainly pottery, this building can be dated to period IV