Complex sentence: A recumbent circle is formed principally of a ring of stones, like all other stone circles; however, there is one, large recumbent stone laid on its side, usually flanked by the two largest of the standing stones immediately on either side.
Split into simpler sentences: A recumbent circle is formed principally of a ring of stones, like all other stone circles; however, there is one, large recumbent stone laid on its side. In these, the recumbent stone is usually flanked by the two largest of the standing stones immediately on either side.