Shibboleth: A Templar Monitor, by George Cooper Connor, , at sacred-texts.com
The road from Jerusalem to Susa, the chief treasury of Persia, and one of the favorite cities of the Persian kings, lay in part through the country restored to the Jews by the decree of Cyrus, but after crossing the Euphrates it was entirely in the domain of King Darius. Indeed, a more cautious statement would limit the Jewish country to west of the Jordan.
The Jews attempted, in an embarrassed way, to picket their own country, and to provide passes with which to distinguish their friends. The domain of the Persian monarch was under strict military surveillance, and countersigns were absolutely necessary to travel therein with safety.
Darius lived in daily dread of spies and secret enemies front among the defeated, though not destroyed, Magians. The discipline of the empire was sternly strict, and the slightest suspicion of disloyalty led to captivity and death.