Use of concrete - By perfecting the use of concrete, the Romans were able to construct tall, strong structures, some of which are still standing today and in quite good condition. Concrete in Roman times was made by mixing lime mortar, sand and stones with water; aside from concrete's strength, the ease of transport of these materials made concrete construction viable. Reusable wooden frames were used to set the concrete in the manner required, and once set the concrete surface was often covered with plaster or stone panels.
Use of arches, vaults and domes - The Romans wanted vast indoor spaces in which large numbers of people could comfortably congregate in, and so, to create these large unobstructed spaces, they replaced the old post and lintel system with the arch system. Using arches, barrel vaults, groin vaults and domes, they were able to roof large public buildings like public baths, basilicas and temples.
Use of columns - Columns were used both as functional and decorative architectural elements. Columns regularly featured in Roman temples and basilicas. In Roman temples, unlike the Greek ones, columns did not go around the temple's main chamber; they were embedded in the walls along the sides and back of the chamber. The Romans used the Greek orders, Doric, Ionic and Corinthian, as well as the wholly-Roman Tuscan and Composite orders.
Use of elaborate interior decoration - This was particularly prevalent in late Roman architecture. The decoration was usually non-structural and veered towards the ornate.
Use of mosaics - Mosaics were made of color stone chips set in cements and were used to decorate a wide range of private and public buildings. The Romans created intricate geometric designs, portraits, scenes and so on in mosaic.