produced in small editions as imperial gifts, which are similar to coins, though larger and usually finer in execution. Images in coins initially followed Greek styles, with gods and symbols, but in the death throes of the Republic first Pompey and then Julius Caesar appeared on coins, and portraits of the emperor or members of his family became standard on imperial coinage. The inscriptions were used for propaganda, and in the later Empire the army joined the emperor as the beneficiary. Architecture 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 citybuilding 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. Because of these methods, Roman architecture is legendary for the durability of its construction; with many buildings still standing, and some still in use, mostly buildings converted to churches during the Christian era. Many ruins, however, have been stripped of their marble veneer and are left with their concrete core exposed, thus appearing somewhat reduced in size and grandeur from their original appearance, such as with the Basilica of Constantine. During the Republican era, Roman architecture combined Greek and Etruscan elements, and produced innovations such as the round temple and the curved arch. As Roman power grew in the early empire, the first emperors inaugurated wholesale leveling of slums to build grand palaces on the Palatine Hill and nearby areas, which required advances in engineering methods and large scale design. Roman buildings were then built in the commercial, political, and social grouping known as a forum, that of Julius Caesar being the first and several added later, with the Forum Romanum being the most famous. The greatest arena in the Roman world, the Colosseum, was completed around 80 AD at the far end of that forum. It held