Engaged columns

In architecture, an engaged column is a column embedded in a wall and partly projecting from the surface of the wall, sometimes defined as semi or three-quarter detached. Engaged columns are rarely found in classical Greek architecture, and then only in exceptional cases, but in Roman architecture they exist in abundance, most commonly embedded in the cella walls of pseudoperipteral buildings.

Engaged columns serve a similar function as wall buttresses but are distinct from pilasters, which by definition are ornamental and not structural.

...
Wikipedia