Final answer:
Engaged columns in Roman architecture were used to create a non-structural layer of classical Greek details, (option C) serving as ornamental elements rather than structural supports while adding to the building's aesthetic.
Step-by-step explanation:
The question asks which of these best describes how Roman architects used engaged columns. The correct answer is that Roman architects used engaged columns to create a non-structural layer of correct Greek details. Engaged columns are semi-structural elements that imitate the function of a fully structural column but are often ornamental and adhere to the wall of a building. They can give the impression of a classical architectural style while not necessarily bearing the load of the structure.
Roman architecture is distinguished by innovations such as the use of concrete, the development of the true arch, vaults, and domes. It is noteworthy that the true arch helps to redistribute weight from the top of the arch to the ground, making it a sturdy building tool. Combined with the use of concrete, this allowed for the construction of vaults and domes that created open interior spaces, which was a significant development from the prior post-and-lintel construction.
Nevertheless, engaged columns themselves were more of an aesthetic feature rather than a structural one, thus serving the purpose of adding classical elegance to the Roman structures, including those with architectural advancements like groin vaults and domes.