Constitution 101: What Is Tonnage?

Article I, Section 10, Clause 3 (I-10-3) of the Constitution forbids states from imposing any “Duty of Tonnage” without the consent of Congress.

During the Founding Era, tonnage was a levy imposed on the cargo capacity of ships entering or leaving harbors. As the Constitution’s words indicate, it was a species in a larger class of financial exactions known as duties.

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