Why Shah Abbas I changed the capital from Qazvin to Isfahan
The initial reason that Shah Abbass I decided to move the location of the capital to Esfahan was that the climate of Qazvin did not suit him. Besides astronomers had predicted that the fortune of Qazvin would change into misfortune soon. On the other hand, during a trip to Esfahan, the idea came to the king that Esfahan would be a new, suitable choice for the capital. The fact was that Esfahan was a four-season region that could provide many facilities as the capital and in sharp contrast to Qazvin, which was a city of six-month hot climate and six-month extremely cold, as a climate with a wide range of fluctuations. That is why it was not comparable at all to Esfahan that could produce the best quality roses, with fertile agricultural lands fully enjoyed the Zayandeh Rood.
Another advantage of Esfahan was its geographical centrality, which gave it political priority over Qazvin and Tabriz (the capital before Qazvin). Apart from all these, Esfahan could materialize the king's aspirations for a more Iranian administrative system, and the reinforcement of the infrastructure of power in the Safavid Dynasty. It could also guide caravans, full of merchandise, towards India. The other reasons also can be listed here are as follow:
1. Owing to its unique geographical situation, Esfahan could be an ideal site to settle the capital as a safe zone against the probable invasions of the Ottomans, Uzbeks, etc.
2. Esfahan was located in an area which did not have any recorded account of earthquakes, at least since seven centuries before.
3. Esfahan could enable the Safavids to monopolize the silk trade, thus they could divert Silk Road toward the north-south routes gradually.
4 Esfahan could pave the way for setting up the centralized, administrative system for better prosperity.