The are styrofoam (eface) covered in plaster.

www.foamfactory.com

A steel beam holds up the structure and the styrofoam columns go over the beam, then they plaster over the styrofoam. I have them and they look like real stone.=]

Thanks. They certainly look great

Yes, if I had to do it over again, I would go with a smoother finish because a rough finish collects dirt and then I must powerwash. But from the street or even up close they look real. Do no use plastic columns, they never look right and the extra expense is well worth it. I think it was about 30% more to do it right so for a $1000 project, it will cost you $300 more. If you calculate it out on property value, the plaster columns more than make up for the expense.