The creation of stained-glass came about as glass transparency was trying to be achieved. The Romans' attempt to make flat glass by pouring half-inch thick slabs was unsuccessful, as the wanted transparency could only be achieved by grinding and polishing the cast material. The lack of transparency and the difficulty in making large panes of glass led to the creation of stained-glass windows, which became popular in the Eastern Roman Empire in the early years of the 12th century. Since that time, stained-glass windows have adorned architecture for hundreds of years.