Checks and balances are designed to maintain the system of separation of powers keeping each branch in its place. The idea is that it is not enough to separate the powers and guarantee their independence but the branches need to have the constitutional means to defend their own legitimate powers from the encroachments of the other branches. They guarantee that the branches have the same level of power (co-equal), that is, are balanced, so that they can limit each other, avoiding the abuse of power. The origin of checks and balances, like separation of powers itself, is specifically credited to Montesquieu in the Enlightenment (in The Spirit of the Laws, 1748). Under this influence it was implemented in 1787 in the Constitution of the United States.