How is Montesquieu's concept of the separation of powers incorporated into the U. S constitution?

Montesquieu believed that there should be three branches in a US Government and that each of the three branches would have their own powers. This relates to the constitution because we have our government separated into three different powers: legislative, executive, and judicial. There really isn't much that comes from our constitution that is original. In fact, almost everything in our constitution came from other documents or philosophers. Such as the english bill of rights, the magna carta, john locke's writings, etc.