The altar to the unknown God
Archimandrite Nikifor’s Biblical Encyclopedia
(Acts 17:22). Concerning this altar many explanations have been offered. The Apostle Paul, in his speech before the Athenian Areopagus, says that he saw such an altar at Athens with the inscription: Agnosto Theo. It may be supposed that there were several such altars, and this is how they are said to have originated, according to the testimony of Diogenes Laertius: in his biography of Epimenides he relates that the Athenians, struck by a pestilence and not knowing to which deity to attribute this calamity, led two sheep, one white and one black, outside the city, and in whatever places the sheep lay down upon the ground, they erected altars to the corresponding deities with the aforementioned inscription.
It is quite possible, however, that the inscription referred also to the God of the Hebrews, since the pronouncing of His name was forbidden by the ordinances of the Hebrew lawgiver.