Heracles is depicted resting on a lion skin. Beside him is an olive tree with a quiver fulfilled with arrows. According to the inscription monument was carved in 139 BC to commemorate the victory of Demetrius II Nicator, a Seleucid Greek, over the Parthian king Mithradathes I.
http://heritageinstitute.com/zoroastrianism/behistun/index.htm