Problem Statement: The historic cities in Iran have gone through many ups and downs, and development and decline, due to various internal and external factors. The study of these factors can help find the roots of cultural and social upheavals. The Old City of Narmashir in the southeast of Kerman is one of these Iranian historic cities. According to archaeological and historical documents, Narmashir has expanded from the Sā sā nid Empire (AD 224– 651) to the late Timurid period. However, as the archaeological materials suggest, the population of the city significantly decreased from the Safavid dynasty onwards. Also, The Old City was abandoned after the Afghans attack. Our question is “ what environmental and ecological factors influenced the formation, development, and destruction of the Old City of Narmashir? ” Purpose: The purpose of this study is to explain the role of geographic and ecological factors in the formation, development, and destruction of the Old City of Narmashir through the lens of Kenneth Watt’ s ecological theory. Research Methodology: Data were collected through documentary and field methods. The systematic survey in this site was carried out in July 2014 and was registered in the cultural heritage list. The research method in this paper is analytical. First, the historical documents were studied and analyzed by the “ content analysis” method. Afterwards, the data were analyzed drawing on the five variables in Kenneth Watt’ s ecological theory: “ material, energy, diversity, space and time. Result: According to our data analysis, “ Space” had not only the most effect on the formation and development of the Old City of Narmashir, but also on its departure and decline. “ Material, diversity, and energy” had also a major role. However, there is not much awareness and evidence on the role of “ material” and “ diversity” in the abandonment of the city by its residents. Moreover, “ time” did not play any significant role in the development and destruction of the city. Such changes in Narmashir might as well be affected by non-ecological factors. The authors believe that the ecological factors mostly led to the above-mentioned three phases.