This huge column dedicated to the emperor Trajan and is very near the Pantheon the first ever comic strip that tells a complete story winds its helical way up this large column. It is a landmark and the detail on the column is phenomenal. And it's free to visit.

Technically, Colonna Traiana is a bas relief. It tells the story of the Emperor Trajan's victory in the Dacian Wars. It is about 30 meters high including its pedestal. This is just at the South West corner of the Piazza Venezia and it is another example of beautiful architecture.
It was in fact a vaguely-delineated area abutting the Black Sea, and the Dacians (Getae during that time) resisted being absorbed into the Roman Empire. Two campaigns by Trajan in the first 6 years of the 2nd Century put paid to their resistance.
Close by Trajan's column is the world's first shopping mall, Mercatus Traiani.
These works of Trajan are well worth the visit, and there are even scattered architectural stones that serve well as seats for the tourist, and make a suitable spot, under the trees, to have a picnic or a swig of water.
It's really worth seeing it especially if you're interested in history. Enjoy the visit before you go to the Colosseum. The column itself is over 100 feet tall, with a sculptured fresco that winds around the column (which is said to be 656 feet long with over 2,500 figures). There is an internal staircase that leads to the top.
Going to the place of these columns makes us to realize how tall they really are. Before going there it looked like a tall, but not much column. Only looking to this column in real life we can realize how imposing they were back in the history.
As you can't get up close this is really just something you walk by and snap a picture on your way somewhere else, but it's interesting to see and a cool part of the history.

It probably took about 6 years to make, erected in 113 AD to mark Emperor Trajan's victory over Dacia (Romania), had a statue of Trajan on top originally, but that vanished during the Middle Ages and the then Pope had it replaced by a statue of St. Peter, which is still there now.
I recommend you to visit it and it is free and you dont have to spend anything.