What amendment is the most important and why?

In 1787 delegates from the thirteen states convened in Philadelphia to replace the unwieldy Articles of Confederation with a Constitution to endow the federal government with sufficient power to hold the country together. This short document, which was a result of both high idealism and low political horsetrading, has survived a Civil War and the massive expansion of the country to become the oldest constitution in the world. The Constitution itself, however, merely describes the functions of the federal government. It was left to ten Amendments, known as the Bill of Rights, to protect individual freedoms.