 After six months, Frankl's visa expired and he became desperately ill.In order to apply for US citizenship, he sailed to Cuba – so as to step on "foreign" soil – and reentered the United States as an immigrant.In 1939, with the assistance of Max Wertheimer, Oscar Kristeller (a professor of Italian Renaissance literature), and Erwin Panofsky, Frankl received a position as art historian at the Institute of Advanced Study at Princeton University.