Gardez city is the capital of Paktia province, which is located 122 km south of Kabul and southeast of Afghanistan and on the route of the main branch of the Silk Road from Ghazni to Sindh. The historical castle (Balahisar) and Mirzaka have a special place in this city. In order to know the foundations of the city under study, it is inevitable to review written sources, field studies and environmental surveys. For this purpose, a systematic survey of the area of Gardez city has been carried out in order to collect surface data. In addition, in order to identify the settlement periods of the city, a borehole was dug near the city wall, whose data have been presented and analyzed in the current research. Also, the results of environmental studies were effective in identifying the factors affecting the formation and development of the city. From the ancient sites and the excavation of the square trench number 1 in the historical castle and the investigation of the Mahmoudiyeh hill (number one) and the Nadiryeh hill (number two), numerous pottery works were obtained, these potteries represent the era of the Achaemenids, Alexander the Great, Parthians, and Seleucids. They are Parthian, Sasanian and Islamic. based on findings and ancient works; The historical heritage of this city is more than what was imagined, this city has been a suitable place for settlement and residence from the geographical and environmental point of view since prehistoric times until now. The location of this area in the four communication routes from west to east and north to south has been one of the other reasons for the establishment and expansion of Gardez city.