The world heritage site of Taq-e Bostan (Arch of Bostan), is more like a historical art gallery with bas reliefs which span centuries.

The main arch contains fantastic reliefs of the Sassanian Kind Khosrow II (591-628 AD).
His investiture is shown in the top part of the arch with Ahura Mazda on his right and Anahita on his left. See also the Temple to Anahita in Bishapur.
Beneath, Khosrow is portrayed in full battle armour on his favourite charger Shabdiz.
On either side of the arch there are hunting scenes, one depicting the imperial boar hunt and the other scene showing the king stalking deer.
On the front of the arch the tree of life is depicted together with two angels holding diadems.
1300 years later, the Qajar governor of Kermanshah decided to "get in on the act" and portrayed himself in bas relief in the main arch.

The smaller arch at Taq-e Bostan portrays Shapur III on the left with his grandfather Shapur II (the Great)on his right.

The investiture of Ardashir II is shown to the right receiving the ring of Kingship from Ahura Mazda.
The Roman Emperor Julian is shown beneath the feet of Ardashir II who he defeated and killed in 363 AD.
Of particular interest is Mithra standing on a lotus flower and holding a Barsam.
As always Mithra is portrayed with the undying son behind his head.
Links to Mithra have been found in many religions including the Roman Mithraism (Sun God) and Manichaeism.

What is particularly wonderful about visiting Taq-e-Bostan is the easy access to the sight.
It's a very small site and many visitors pass through quite quickly perhaps a little disappointed.
Much better to spend a while and examine the intricate details of the reliefs through binoculars, particularly the hunting scenes.

The photographic technique used to enhance the bas reliefs is described here.