In its 2015 announcement, the MacArthur Foundation said that she had been given the 625,000 prize for "deploying her considerable prowess in languages, social history, and papyrology", and that Rustow is "rewriting our understanding of medieval Jewish life and transforming the historical study of the Fatimid empire". Rustow said that "The award is going to permit me to work in a way that I haven't really been able to work before," and "to dig a little bit deeper".
Academic research
In her 2008 book Heresy and the Politics of Community: The Jews of the Fatimid Caliphate, Rustow challenged conventional wisdom about the relationships between two rival Jewish communities living under the Fatimid Caliphate from 909 to 1171 C.E. They were the mainstream Rabbanites and the Karaites, who reject the authority of the Talmud and rely only on the Hebrew Bible. Most previous historians had described them as "factions bitterly divided by theological difference, the latter branded as heretics and marginalized." Rustow studied everyday documents that were part of a massive archive at the Ben Ezra Synagogue in Old Cairo. These documents, such as contracts, letters and government decrees and petitions, showed "a wealth of social, economic, and political transactions between the two groups". Her book calls into question "the depth of the religious schism, suggesting a higher level of tolerance and cooperation than had been assumed". Previous scholars of documents found in the Cairo geniza had concentrated on texts written in Hebrew and Aramaic. Rustow chose to study those written in Arabic, which often appear "in the margins and on the backs of such documents." Her studies with colleagues have led to insights about the everyday lives of the Jews of Cairo, such as that they "imported sheep cheese from Sicily—it was deemed kosher—and filled containers at the bazaar with warm food in an early version of takeout." There was a triangular Mediterranean trade route between Egypt, Tunisia and Sicily in the 11th century, and flax used to make linenfabric, and soap, were the main commodities. "Everyone wore linen all the time," according to Rustow. She is studying the usage of the Arabic language by the Jews of Sicily in years following the expulsion of Muslims·from Sicily in the 13th century C.E. The Muslims had previously ruled Sicily from the 9th century to the 11th century. In collaboration with Sacha Stern, she has also done research on the Jewish calendar, focusing on the 10th century C.E. dispute between Jewish authorities Aaron ben Meïr and Saadia Gaon about the calendar.