Which Roman emperor was best known for his extensive public building program?

Trajan (Imperator Caesar Nerva Traianus Divi Nervae filius Augustus;18 September 53 – 8 August 117) was Roman emperor from 98 to 117.

Officially declared by the Senate optimus princeps ("the best ruler"), Trajan is remembered as a successful soldier-emperor who presided over the greatest military expansion in Roman history, leading the empire to attain its maximum territorial extent by the time of his death.

He is also known for his philanthropic rule, overseeing extensive public building programs and implementing social welfare policies, which earned him his enduring reputation as the second of the Five Good Emperors who presided over an era of peace and prosperity in the Mediterranean world.

Trajan was a prolific builder in Rome and the provinces, and many of his buildings were erected by the gifted architect Apollodorus of Damascus. Notable structures include the Baths of Trajan, Trajan's Forum, Trajan's Column, Trajan's Bridge, Alcántara Bridge, Porto di Traiano of Portus, the road and canal around the Iron Gates. In order to build his forum and the adjacent brick market that also held his name Trajan had vast areas of the surrounding Capitoline and Quirinal hills leveled.