I started [in 1921] to write on the foundations of an approach to international trade theory that was to some extent new and for which I received the inspiration during a stroll on [the popular promenade] Unter den Linden in Berlin in 1920.

Ohlin in his memoirs, as cited in: Flam, Harry, and M. June. "The Young Ohlin on the Theory of Interregional and International Trade." Bertil Ohlin: A Centennial Celebration, 1899-1999 10 (2002): p. 175.