The structure is about 30 meters (98 ft) in height, 38 meters (125 ft) including its large pedestal. The shaft is made from a series of 20 colossal Carrara marble drums, each weighing about 40 tons, with a diameter of about 4 meters (13 ft). The 190 meter (625 ft) frieze winds around the shaft 23 times. Inside the shaft, a spiral staircase of 185 stairs provides access to a viewing platform at the top.
According to coins depicting the column, it was originally topped with a statue of a bird, possibly an eagle, and later by a heroically nude statue of Trajan himself which disappeared in the Middle Ages. In 1588, it was replaced by a statue of St. Peter (which still remains), commissioned by Pope Sixtus V.
The relief portrays Trajan's two victorious military campaigns against the Dacians; the lower half illustrating the first (101-102), and the top half illustrating the second (105-106).
The two sections are separated by a personification of Victory writing on a shield flanked on either side by Trophies. Otherwise, the scenes on the frieze unfold continuously and in tipped-up perspective. The imagery is not realistic as the sculptor pays little attention to perspective. Often a variety of different perspectives are used in the same scene, so that more can be revealed (e.g. a different angle is used to show men working behind a wall).
The scenes depict mostly the Roman army in military activities such as setting out to battle and engaging the Dacians, as well as constructing fortifications and listening to the emperor's address. The carvings are crowded with sailors, soldiers, statesmen and priests, showing about 2,500 figures in all and providing a valuable source of information for modern historians on Roman and barbaric arms and methods of warfare (such as forts, ships, weapons etc.). The relief shows such details as a ballista or catapult for example. The emperor Trajan, depicted realistically (not superhuman), makes 59 appearances among his troops. A large figure of a river god is also visible.
The base is covered with reliefs of trophies of Dacian weapons. Such imagery had the connotation of a surrender, as in Ancient times the defeated soldiers would dump their weapons in a pile as a term of surrender.
The inscription at the base of the column in finest lettering reads:
Translated, the inscription reads:
The Senate and people of Rome [give or dedicate this] to the emperor Caesar, son of the divine Nerva, Nerva Traianus Augustus Germanicus Dacicus, pontifex maximus, in his 17th year in the office of tribune, having been acclaimed 6 times as imperator, 6 times consul, pater patriae, to demonstrate of what great height the hill [was] and place [that] was removed for such great works.
It was believed that the column was supposed to stand where the saddle between the Capitoline and Quirinal Hills used to be, having been excavated by Trajan, but excavation has revealed that this is not the case. The saddle was where Trajan's Forum and Trajan's Market stood. Hence, the inscription refers to the Trajan's entire building project in the area of the Imperial fora.
This is perhaps the most famous example of Roman square capitals, a script often used for stone monuments, and less often for manuscript writing. As it was meant to be read from below, the bottom letters are slightly smaller than the top letters, to give proper perspective. Some, but not all, word divisions are marked with a dot, and many of the words, especially the titles, are abbreviated. In the inscription, numerals are marked with a titulus, a bar across the top of the letters. A small piece at the bottom of the inscription has been lost.
The typeface Trajan, designed in 1989 by Carol Twombly, uses letterforms based on this inscription. There have been many other typefaces based on the inscription from such designers as Frederic Goudy.
It was traditionally thought that the Column was a propagandistic monument, glorifying the emperor's military exploits. However, the structure would have been generally invisible and surrounded by the two libraries in Trajan's Forum, and because of the difficulty involved in following the frieze from end to end, it could be said to have had much less propaganda value.
On the other hand, as Paul Veyne notes, the relief could be read "vertically" from below, with the stereotypical, highly recognizable figure of the emperor recognizable across the bands of images— just as, on the Colonne Vendome, Napoleon's figure can be picked up, scene after scene.
After Trajan's death in 117, the Roman Senate voted to have Trajan's ashes buried in the Column's square base which is decorated with captured Dacian arms and armor. His ashes and those of his wife, Plotina, were set inside the base in golden urns. (The ashes no longer lie there.)
Plaster casts of the relief were taken in the 19th and 20th centuries. Ironically, after a century of acid pollution, they are now more legible in some details than the original and, even when not, offer students a closer look at the reliefs because of the way they are displayed. Examples can be seen at: