Iranian Bridge-Caravansaries Evolutionary process of unifying Caravansary buildings and Bridge structures

Expansion of communication routes to conquer new lands and trade goals are part of the progression process of various civilizations. Iranians with its strategic position in Silk Road tried to build roads and road side facilities such as bridges to pass natural barriers, posts and caravansaries as resort centers and a place to provide passenger needs like food, water and feed. Beginning of the road construction and side facilities starts at Achaemenid era. During this era, security and support facilities show a dominant management. During Parthian era, second Mithridat tried to expand commercial relationships with china and Europe. Changing world commercial condition during crusades speeds up and Iran became the junction point of Eastern and western civilizations. The peak of this can be seen in Safavid era. Important routs are main international, pilgrimage roads and domestic less important roads. But most of bridges are constructed in northern and western mountainous situations of Iran plateau. This process changed in the late Safavid era that maritime grows and reduced the importance of Iran as a strategic connection point in world trade. In Iranian Bridges we have numerous examples, that bridges have been used for two as a passageway and a place to stay. Embedded blank spaces over stone bases and arches, connection points between bridge and banks and underside pass level are used at first examples as a temporary place for builders, a place to store construction materials, guard shelter and eventually as a rest area for travelers and their horses. This study aims to demonstrate Iranians innovation to merge two functions and reduces them into a united construction volume. This create a favorable conditions for travelers resort station and from analytical point of view research tries to show design method and structural capabilities of bridges to providing spaces and a historical review to appeal evidence of their evolution from a simple empty space to a methodology for designing bridges. At first a comparative study shows the structural capabilities of Persian bridges than roman bridges to shows their capabilities to create vast empty spaces. Evolutionary process of these spaces begins with utilize a vast empty space due structural relations and lead to an important factor during design and construction process. Results show that Iranian innovation in construction of "resort-bridge" structures at first with the aim of providing water for people living in the inn, reducing the volume of construction volume in poor condition of countries, reducing bad working condition and reduce the volume of construction material usage to minimize the pressure loads on bases, use of suitable climatic conditions of rivers. Historical evidence shows that a simple functional trend became to an aesthetical point of views that created great masterpiece of Safavid era. During this era and in inner city bridges, previous thoughts became a model to building bridges with recreation facilities. Jooyi, Allahverdikhan and Khajoo Bridges are the best sample of aesthetical viewpoint of this evolutionary process. During Qajar era, only two bazaars were constructed on Tabriz inner city bridges.