A pilaster is nothing more than a column cut in half and then placed against the wall.
It is not a load-bearing element like a column, it is decorative only.
However, a pilaster must appear to be supporting another architectural structure. In this example the pilaster is supporting an architrave, also a decorative architectural element.
You can use pilasters in the corner of rooms, mid-wall, integrated with wainscoting, on stairs or, like the ones here, flanking an archway.
These pilasters are located inside the gothic revival (or “Traditional,” in my simplified style definitions) First Presbyterian Church in Royal Oak, Michigan.
I found them while helping the Reuter Organ Company install the church’s new en chamade (external link), and so thought I’d share them with you.
Supporting the Architrave
The most common structure for a pilaster to support is the architrave portion of the entablature. Or, your crown molding.
These pilasters are fiberglass and can be purchased from many different online companies. They are not terribly expensive.
But if you’d like to build your own, like I did for a previous project, there is a whole step by step tutorial here: How to Make PILASTER-104 for About $13.61 each.