This very impressive solid wood mirror is what's known as a "parcloses mirror". It consists of a large mirror surrounded by smaller ones. They are held in place by a decorative intermediate frame (or enclosure, which gave rise to the name "parcloses"). In the past, this technique enabled the size of the mirror to be enlarged with smaller pieces.
This mirror dates from the second half of the 19th century, a period when neo-Gothic and neo-Renaissance styles came back into fashion in architecture, furniture and even literature.
You can choose to hang it vertically or horizontally, depending on your space, but either way it's sure to catch the eye.