Stained-glass windows become very popular. This would have added to the already dramatic lighting found in churches (like Hagia Sophia). Remember that light is a symbol of God's presence. What better art could have been made at this time than art which could literally light up in the sun and radiate its colorful splendor in the church.
Another element added to churches was flying buttresses, which is a hilarious name for the supporting columns on the outside of the main infrastructure. Quasimodo slides down Notre Dame's flying buttresses in the Disney version of Hugo's The Hunchback of Notre Dame.