What did the Persians do to create a large and long-lasting empire?

The Persian Empire lasted as long as it did, and got as big as it did, because it was fairly loosely governed. The Empire, which stretched from North Africa to the Balkans to India at its greatest extent, was in many ways a loose collection of territories, each governed by a royally-appointed governor, or satrap. While the Persians would gain a reputation for despotic rule (mostly stemming from their war with the Greeks) they were...

The Persian Empire lasted as long as it did, and got as big as it did, because it was fairly loosely governed. The Empire, which stretched from North Africa to the Balkans to India at its greatest extent, was in many ways a loose collection of territories, each governed by a royally-appointed governor, or satrap. While the Persians would gain a reputation for despotic rule (mostly stemming from their war with the Greeks) they were in reality tolerant rulers, usually choosing not to impose their religion and culture on the peoples (the Jews in Mesopotamia and the Levant, for example) they ruled. They were more interested in fostering and profiting from trade between various parts of the Empire. At the same time, the Persians expended considerable energy on public works, including roads that connected various parts of the Empire, and they were fairly efficient at extracting tax revenue from the peoples they ruled. So the Persian Empire was flexible and capable of adapting its governing style and policies to the very diverse people that fell under its rule.