The Dome of the Rock in Jerusalem is another excellent example of Islamic architecture. Finally, the impact of Islamic architecture may be observed in Cairo, Egypt. Extroverted building is a type of Islamic architecture that has windows that look out into streets whenever feasible (Islamic Architecture in Cairo). Islamic art also influenced European art. The artistry of Muslim builders was often used to decorate churches in Europe during the Crusades and later during European trade settlements with Asia. For example, many Gothic cathedrals have extensive use of turquoise, red sandstone, and other exotic materials from the Middle East. Finally, modern art is also influenced by Islam. Some artists such as M. C. Escher are known for their imaginative depictions of objects that appear to be impossible or at least difficult to create. In addition, some critics believe that Paul Cézanne's work on painting color between 1855 and 1865 had an important influence on abstract expressionism in the twentieth century. Cézanne is also responsible for bringing attention back to the study of light and vision in paintings. Previously, artists focused more on physical reality than on vision itself. They would paint what they saw before them, but it was up to others to interpret this reality for them. Cézanne changed all this by insisting that you must understand how vision works if you want to capture its magic on canvas or paper.