From the symbolic point of the view the porch has the effect of separating what is below from what is above through its roof and defining a point on earth through its sides. It thus aids man in defining a position for himself both in relation to his Deity and in relation to his space. The concept manifests itself under two additional forms forms, 'Talar' and 'Mehrab'. Both of these have the same effect of defining a position for man in relation to his space.
The development of the Eivan as a form can be traced from the Achamaenid tradition through Arsacid or Parthian palaces to the Sassanid period during which it was used extensively. It is thus a pre-Islamic form which was well established prior to the conquest of Iran by the Arabs in the mid-seventh century CE. The Eivan illustrated here is from the Friday Mosque (Masjed-e-Jomeh) and demonstrates the connection between the courtyard and the Sanctuary. By its size and harmony we can perceive it as the externalisation of divine might which gives form and substance to man's place on earth
An Eivan thus represents the Connection, while its barrelled vault represents the Transition and whatever lies beyond is seen as a Culmination.