ules have foals" was equivalent in those days to
our proverbial phrase, "when the sky falls," being used to denote any
thing impossible or absurd, inasmuch as mules, like other hybrid
animals, do not produce young. It was thought in those times
absolutely impossible that they should do so; but it is now well known
that the case is not impossible, though very rare.

It seems to have added very much to the interest of an historical
narrative in the minds of the ancient Greeks, to have some prodigy
connected with every great event; and, in order to gratify this
feeling, the writers appear in some instances to have fabricated a
prodigy for the occasion, and in others to have elevated some unusual,
though by no means supernatural circumstance, to the rank and
importance of one. The prodigy connected with this siege of Babylon
was the foaling of a mule. The mule belonged to a general in the army
of Darius, named Zopyrus. It was after Darius had been prosecuting the
siege of the city for a year and a half, without any progress
whatever toward the accomplishment of his end. The army began to
despair of success. Zopyrus, with the rest, was expecting that the
siege would be indefinitely prolonged, or, perhaps, absolutely
abandoned, when his attention was strongly attracted to the phenomenon
which had happened in respect to the mule. He remembered the taunt of
the Babylonian on the wall, and it seemed to him that the whole
occurrence portended that the time had now arrived when some way might
be devised for the capture of the city.

Portents and prophecies are often the causes of their own fulfillment,
and this portent led Zopyrus to endeavor to devise some means to
accomplish the end in view. He went first, however, to Darius, to
converse with him upon the subject, with a view of ascertaining how
far he was really desirous of bringing the siege to a termination. He
wished to know whether the object was of sufficient importance in
Darius's mind to warrant any great sacrifice on his own part to effect
it.

He found that it was so. Darius was extremely impatient to end the
siege and to capture the city; and Zopyrus saw at once that, if he
could in any way be the means of accomplishing the work, he should
entitle himself, in the highest possible degree, to the gratitude of
the king.

He determined to go himself into Babylon as a pretended deserter from
Darius, with a view to obtaining an influence and a command within the
city,