Its most prominent features included the use of the rib vault and the flying buttress, which allowed the weight of the roof to be counterbalanced by buttresses outside the building, giving greater height and more space for windows. Another important feature was the extensive use of stained glass, and the rose window, to bring light and color to the interior. Another feature was the use of realistic statuary on the exterior, particularly over the portals, to illustrate biblical stories for the largely illiterate parishioners. Some key architectural features, such as the pointed arch and a decorative kind of rib vault, existed earlier outside Europe, and may have been derived from Islamic architecture. These features had both existed in Romanesque architecture, but they were used more extensively and in more innovative ways to make Gothic cathedrals higher, stronger, and filled with light.