Many Dutch architects migrated to the rapidly developing Dutch East Indies in the early twentieth century. It was the "golden period" of Dutch architecture in the tropics. Cosman Citroen (1881-1935) largely determined the face of Surabaya, Indonesia's most important trading center. His town hall ties tradition to modernity and, with galleries and a double roof, is perfectly suited to a tropical climate. Citroen's last design, the office building for Borsumij, is a paragon of modernity: rectangular with a flat roof, executed in concrete skeleton with wide window strips. Because of his training, Citroen had partly an arts and crafts background, as can be seen well in the luxurious interior of the Tan Tjwan Bie villa, where he also designed the teak ceilings and paneling, as well as the hanging lamps, stained glass and the floor with unusual geometric patterns.