This theater relief depicts the sacred marriage of PersephoneKore (the daughter of the goddess Demeter) and the god of the Underworld, Pluto. According to mythology, this "event" took place in the region of Nysa.
On the left side of the panel, the geographic setting of the abduction of Kore is depicted—mountain, spring, and river. On the left, there is a standing nymph. Reclining below her is a river nymph holding an overflowing spring vessel. Above her is a mountain god Mesogis. The river god, Meander is reclining with the Meander River flowing from his vessel (Nysa is located on a slope overlooking the Meander Valley to the south of it). In the center (just to the left of the seam) is Tyche, with a crown of city walls that represents the city of Nysa.
On the right side, Kore is depicted as fleeing from Pluto with her head turned back towards him. A small Eros keeps her from escaping. Pluto, with the upper part of his body exposed, is grasping her with his left hand. The inflated "cloaks" behind them may represent haste, surprise, or more probably divine status—compare the reliefs on the Sebasteion at Aphrodisias. On the far right is Pan, with goat legs—he was always pursuing females!
The description above is an abbreviation of the commentary offered by Egisto Sani on a similar picture on his flickr account. He in turn is dependent upon the original work of Ruth Lindner, "Mythis und Identität."
Lindner, Ruth. Mythos Und Identität: Studien Zur Selbstdarstellung. Stuttgart: Steiner, 1994.