Complex sentence: Ninomaru Garden and what is presently known as Ninomaru East Garden were once part of the Ninomaru Palace grounds and said to have been built between 1615 and 1623, when Ninomaru Palace was constructed.
Split into simpler sentences: Ninomaru Garden and what is presently known as Ninomaru East Garden were once part of the Ninomaru Palace. It is said to have been built between 1615 and 1623, when the Ninomaru Palace was constructed.