The Column of Trajan functions as a

monumental gate

tribute to the Roman deities

religious monument

propagandistic memorial

I believe the correct answer is the last option: propagandistic memorial.

Column of Trajan is a Roman triumphal column constructed by the architect Apollodorus of Damascus, located in Rome, Italy, which commemorates Roman Emperor Trajan's victory in the Dacian Wars. According to the traditional scholarships, Column was a glorifying monument whit propagandistic function as describes epic wars between Romans and Dacians and it also upholds Trajan as Rome's great emperor.