Gothic cathedrals
With pointed arches, windows could be made very large. Architects made many designs of pointed arches crossing each other in different ways. These designs were often used in windows, which look as if they are filled with beautiful stone lace. This is called "tracery". The stone tracery was used to hold the glass in place. An Architectural Historian can often tell just how old a part of a building is by looking at the window tracery design.