The city of Rey was one of the most prominent and prosperous cities of the Islamic world during the early to middle centuries of the Islamic period. Several factors had influenced this prosperity and importance. The main objective of this research is to find out the specific factors, among others, which had affected the prosperity of roads and the relationship between roads, economics, and the spatial structure of Rey. For this, the reasons for the significance of the roads of Rey in the early centuries of Islam up to the Mongol invasion are identified from historical texts. Then, the development of the city from an architectural and urban perspective is examined through a comparative study of numerous historical texts as well as historical and archaeological studies of contemporary scholars. Based on the results, the mutual relationship between the road network and the spatial structure of the city is drawn in the given period. Based on the findings of this research, adequate security, ample water resources, as well as the centrality and importance of the city from a commercial and religious point of view had led to the constant presence of merchants and caravans in Rey. The beauty, cleanliness, and the existence of numerous caravansaries, baths, and high-quality markets, added to the welfare of travelers and merchants. In addition, a number of goods produced in Rey were largely popular and easily sold in the markets of other lands. These factors increased the affluence of the city and market stability due to numerous commercial exchanges besides the safety and welfare of travelers and merchants. In the end, the relationships between the natural and the spatial structure of the city and its roads are seen as reciprocal within a cycle.