During one of my first Timber Framers Guild Conferences, I heard a talk by Vico Von Voss about his various projects. He referred to square timbers as the male form and round timbers as the female form, and that you need to have a balance between the two in a frame. This was a powerful message that I took to heart, incorporating this theory into my own home as well as many projects for clients as possible.
This joinery detail is an example of using round posts and square beams to achieve a truly unique look. While it looks difficult to cut, with some basic skills and theory you can do it as well. The key is to use the scribing method along with string lines to help with visualizing that there is a square timber inside of the log. Scribing involves laying out and transferring round or square joinery connections from one timber to another using levels, plumb bobs and scribing tools instead of more modern methods.
While it does take more time and patience, the look is well worth the effort. If you need some help there are classes out there it help you out. One class to help teach you this technique is found at the Heartwood School.