Ancient Rome is renowned for its architecture, especially its use of the arch and concrete -- seemingly small items -- that made possible some of their engineering feats, like aqueducts built with rows of graceful arches (arcades) to carry water to cities more than fifty miles away from area springs.
Here are articles on architecture and monuments in ancient Rome: the multipurpose forum, the utilitarian aqueducts, heated baths and sewer system, residences, monuments, religious buildings, and spectator event facilities.

"A History of Rome," by Robert Fowler Leighton. New York: Clark & Maynard. 1888There were actually several fora (plural of forum) in ancient Rome, but the Roman Forum was the heart of Rome. It was filled with a variety of buildings, religious and secular.
This article describes buildings listed in a drawing of the reconstructed ancient Roman forum.

History ChannelThe Roman aqueduct was one of the ancient Romans' main architectural accomplishments.
This article, by guest writer Al Schlaf, describes the aqueducts built during the reign of Augustus.

Public Domain. Courtesy of Lalupa at Wikipedia.The Roman baths were another area where Roman engineers showed their ingenuity figuring out ways to make hot rooms for the public social gathering and bathing centers. The Baths of Caracalla would have accommodated 1600 people.
In ancient Rome most city people lived in several story-high fire traps.

Judith GearyOn
this page from her longer article on Republican Roman construction, writer Judith Geary shows the layout of the typical Roman home in Republican times and describes the homes of the earlier period.
The Mausoleum of Augustus was the first of the monumental tombs for the Roman emperors. Of course, Augustus was the first of the Roman emperors.
Trajan's Column was dedicated in A.D. 113, as part of Trajan's Forum, and is remarkably intact. The marble column is almost 30m high resting on a 6m high base. Inside the column is a spiral staircase leading to a balcony along the top. The outside shows a continuous spiral frieze depicting events of Trajan's campaigns against the Dacians.
Agrippa originally built the Pantheon to commemorate the victory of Augustus (and Agrippa) over Antony and Cleopatra at Actium. It burned and was rebuilt and is now one of the most impressive monuments from ancient Rome, with its giant, domed vault with an
oculus (Latin for 'eye') to let in light.

Ancient Rome in the Light of Recent Discoveries," by Rodolfo Amedeo Lanciani (1899).The Temple of Vesta held the sacred fire of Rome. The temple itself was round, made of concrete and was surrounded by close columns with a screen of grill-work between them. The Temple of Vesta was by the Regia and the house of the Vestals in the Roman Forum.
The Circus Maximus was the first and the biggest circus in Ancient Rome. You wouldn't have attended a Roman circus to see trapeze artists and clowns, although you might have seen exotic animals.
Pictures of the Colosseum
The Colosseum or Flavian Amphitheater is one of the most well-known of the ancient Roman structures because so much of it still remains. The tallest Roman structure -- at about 160 feet high, it is said to have been able to hold 87,000 spectators and several hundred fighting animals. It is made of concrete, travertine, and tufa, with 3 tiers of arches and columns different orders. Elliptical in shape, it held a wooded floor over the underground passageways.
Source : Colosseum - From Great Buildings Online