When I heard him explain how the founders foresaw this need to go around Congress and enable the states on their own to call a Constitutional Convention, I was once again awed at the brilliance of those men. But in actuality, it was one man who really pushed for the ability of the states to be able to call a convention (I can't recall who ATM) - but he convinced others to add it. And thank God!

Article 5: The Congress, whenever two thirds of both Houses shall deem it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments, which, in either Case, shall be valid to all Intents and Purposes, as Part of this Constitution, when ratified by the Legislatures of three fourths of the several States, or by Conventions in three fourths thereof, as the one or the other Mode of Ratification may be proposed by the Congress; Provided that no Amendment which may be made prior to the Year One thousand eight hundred and eight shall in any Manner affect the first and fourth Clauses in the Ninth Section of the first Article; and that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate.