The elements that make up the physical structure of cities are transformed over time. One of these important elements was the defensive wall of cities. Depending on the circumstances of each historical period, it has changed. In addition to the security role of this element, it is also very important to influence the expansion of the city. Yazd is one of the most valuable historical cities in the country, which Until the Timurid era, the defensive wall was one of the main factors in its development. Today, there are parts of the Mozaffarid and Timurid walls and the gates of these eras in the city; but despite evidence and written documents, there are still unanswered questions about the development of the fortification and the closure of the gates. Among these questions, what was the date of formation and development of the historic city of Yazd? What has been the location of the gates of the historic city of Yazd and the changes related to their location throughout history? The present article aims to reflect existing evidence, by studying library documents, surveying, and finally, analyzing the content of existing documents. Understanding changes in the shape of fortifications over time is important in gaining an understanding of the physical structure of historic cities. The achievement of the existing study indicates, the location of the Mehrijerd gate has changed from Kakuid to Mozaffarid era. Also, the initial location of the Mehrijerd gate, the gate of Bob Kia ,and the Kushkeno gate for archaeological speculation were obtained. The maps from the development of fortification during historic periods also indicate the significant effect of this artificial factor on the physical structure of the city and its developmental form.