The Tragedy of Antony and Cleopatra Act IV, Scene iii Summary

That night, as Antony’s soldiers stand watch and chat about the coming battle, strange oboe music begins to play. It seems to come from the air and the earth simultaneously.
The men guess it is the sound of Hercules (the god Antony modeled himself after and claimed as his ancestor) leaving Antony, which is not so good of a sign for the upcoming battle.