The duty of the legislative branch is to make the laws. Congress is the only branch of the U.S. government that existed prior to the Constitution, although it took a different form. The framers of the Constitution expected that Congress would overshadow the newly created executive and judicial branches, and they spelled out its powers in considerable detail. They also placed explicit limits on the powers of Congress, to balance its weight against the other branches. Thus, Article I is the longest part of the Constitution—longer than Articles II and III combined, which cover both the executive and the judiciary. Article I contains the laundry list of federal powers—among them to collect taxes, borrow money, regulate commerce, establish post offices, and declare war. It also allows Congress to make all laws “necessary and proper” for carrying out the powers specifically granted, a broad source of authority in the modern regulatory state. Article I holds two compromises that were essential to the formation of the Union: equal representation of the states in the Senate, and the valuation of a slave as three-fifths of a person.

This earliest photograph of the Capitol was taken in 1846, before a larger dome and expanded wings were built.