Garden Bed

I was intrigued by these planters, which are outside the Portland Village School. I was wondering if I could do something like this for the herb bed I was planning to build out front.

Nice joining.
But this is the cool part. They seem to have been fastened with a metal rod of some sort.
The rod goes all the way to the bottom.
Very nicely done, but I concluded that they were beyond my carpenter capabilities at this point.