Which architectural order is defined by fluted columns, smooth capitals, and no base?

The correct answer is the Doric order, which is characterized by its distinctive features. The Doric column is typically fluted with deep vertical grooves, which enhances its visual texture and helps to give it strength. One of the defining aspects of the Doric order is that it has a simple, unadorned capital that is generally smooth—often just a square slab or a rounded section without elaborate decoration. Additionally, Doric columns rest directly on the stylobate without a separate base, setting them apart from the other classical orders which typically feature a base as part of their design.

The Ionic and Corinthian orders have different characteristics that differentiate them from the Doric. The Ionic order is known for its volutes or scroll-like decorations on the capital and includes a base. The Corinthian order, while it incorporates fluted columns like the Doric, is more elaborate, with an ornate capital that features acanthus leaves. The Composite order is a later development that combines elements of both the Ionic and Corinthian styles, also featuring a base and more intricate capital designs.

The specificity of the Doric order in terms of its column design makes it the correct answer for the defining characteristics listed in the question.