Complex sentence: The plans of the tower were altered so that it would hold a library, instead of being purely ornamental, windows were added at regular intervals, and it was topped by a copper flèche, or small spire.
Split into simpler sentences: The plans of the tower were altered so that it would hold a library, instead of being purely ornamental; windows were added at regular intervals. It is topped by a copper flèche, or small spire.