I don't know for sure but here's a quote from a blog entry about Marjane Satrapi.
"I think Marjane Satrapi’s surname may be derived from the satrapy system of Ancient Persia. But what is this system, you ask? Well, after Cyrus the Great had established the Persian empire through the conquest of Media, Lydia, Babylon and so forth, he needed a way of administering it. So organised them as satrapies, which were essentially provinces. These were governed by satraps who represented the king, to whom they were directly responsible. Important satrap posts – eg Babylon, Egypt, Lydia – were often given to princes. Others were given to Persian nobles, who sometimes had the position for life. Some positions became hereditary. Satraps organised the economy, justice system, the collection of taxes/tributes and military levies when needed. Regional governors were often in charge of smaller areas under the satrap of their particular province. By Darius’ time there were approximately 20 satrapies. It’s hard to say exactly as different sources provide differing lists in various times; Darius mentions 29 groups that pay tribute in the Naqsh-i Rustam Inscription."http://feminismsfordummies.wordpress.com/2009/09/04/its-history-lesson-time/