Congress originally proposed twelve constitutional amendments in 1789 before the Bill of Rights was ratified.
The First Congress approved the twelve proposals on September 25, 1789, after James Madison organized recommendations submitted by the states and members of Congress. The proposals were sent to the states for consideration as additions to the Constitution rather than as changes to its existing text.
Only ten were ratified by December 15, 1791, becoming the First through Tenth Amendments and collectively known as the Bill of Rights. The original first proposal, concerning the size of congressional districts, remains unratified. The original second proposal, concerning congressional pay changes, was finally ratified in 1992 as the Twenty-seventh Amendment.
This history explains why the Bill of Rights contains ten amendments even though twelve were initially submitted. It also shows that the amendment process can remain open for generations when Congress does not impose a ratification deadline.