The gate operates within that steel frame. The frame was secured to the stone columns w large masonry screws . The columns are supported by 8' piers. The gate still operates wonderfully.

Thank you so much for your helpful answer. I'm happy to know the gate works well.

Now I need to learn about stone pillars, their construction, and the recommended sizes and ratios to strength of support as well as if and how they might work in my limited space and within particular conditions here.

I recommend you hire a contractor! That's what they do!

Thank you! I will.

(Also, I finally saw my typing error in my above message. It is too late to correct it.)