Short answers, pulled from the story.
Roman artists began importing vast numbers of statues as booty or through commerce after the conquest of Corinth in 146 BC. This trade moved briskly throughout the empire during the first century BC.
The best known pocket of surviving wall paintings comes from Pompeii and Herculaneum where residents decorated their walls before Mount Vesuvius erupted in AD 79. These sites reveal how wealthy seaside resort residents adorned their homes with art.
Trajan's Column presents realistically rendered individuals including over 2,500 figures plus landscapes animals ships and other elements. This unprecedented achievement spans over 190 meters of spiraling length to record the Dacian wars conducted by Trajan.
Trajan reigned from 98 to 117 AD when Rome reached peak artistic glory through massive building programs. Hadrian ruled from 117 to 138 AD continuing these grand initiatives such as the Baths of Diocletian and the Baths of Caracalla.
In the 3rd century Roman art largely abandoned sculpture in the classical tradition entirely showing stumpy large-eyed figures in harsh frontal style. Even most important imperial monuments showed features and drapery folds rendered through incisions rather than modeling instead.