Give a stream of consciousness and then the final answer. It was in the area of architecture that Roman art produced its greatest innovations. Because the Roman Empire extended over so great of an area and included so many urbanized areas, Roman engineers developed methods for city building on a grand scale, including the use of concrete. Massive buildings like the Pantheon and the Colosseum could never have been constructed with previous materials and methods. Though concrete had been invented a thousand years earlier in the Near East, the Romans extended its use from fortifications to their most impressive buildings and monuments, capitalizing on the material's strength and low cost. The concrete core was covered with a plaster, brick, stone, or marble veneer, and decorative polychrome and gold-gilded sculpture was often added to produce a dazzling effect of power and wealth.

Based on this passage, in which form of art were the romans most innovative?
To answer the question, consider the following: It was in the area of architecture that Roman art produced its greatest innovations.
So, the final answer is architecture.