Architecture and building design is a unique and less recognized form of art. During the Industrial Revolution, swarms of people living in the countries were driven into the cities. This rapid urbanization lead to extreme over population. Immense pressure was put on cities’ infrastructures causing a need for new buildings and rapid expansion of cities. New and more effective forms of architecture came forward and old themes returned such as the Roman, Greek, and Gothic styles of building. The use of iron was also introduced to architecture. After the Industrial Revolution, three forms of iron became available to builders and architects: cast iron, wrought iron, and steel. With these new forms of strong building components, the art of architecture was greatly changed. Bridges were quickly built to cross rivers to transport supplies and the advent of railroads affected the layouts of cities and architecture as well. All these changes were made to strengthen buildings and support the crowds of people flowing in and working long hard hours with large machines and new technology.