The 1906 Olympic Games were held in Athens, Greece to celebrate the 10th anniversary of the Olympic Games revival (the first was 1896). To publicize this event, Greece issued on March 25, 1906 a set of 14 stamps with 9 different designs. Here they are except two missing designs:
Discus thrower, ancient Greek coin from Kos, ca. 480-475 B.C. Probably god Apollo:

Jumper:

Probably, Nike, goddess of Victory (according to Michel catalogue):

Wrestling between Heracles and Antaeus, design based on an ancient Greek vase artwork, painted by Euphronios in 515-510 BC., Louvre Museum, Paris:

The wrestlers, a Roman marble sculpture after a lost Greek original of the third century BCE. The sculpture is exhibited in the Uffizi Museum in Florence, Italy:

Winged woman holding an hen, probably, Nike, goddess of Victory:

Atlas brings the apples to Heracles while he is holding the sky, ancient Greek amphora:

This set, together with the above 1896 Greek set, are among the jewels in my Greek Mythology stamp collection. Hope to complete them soon since the missing values depicting also figures of Greek mythology.