
53 U.S. 293 (1851)
12 How. 293
JAMES C. ACHISON, PLAINTIFF IN ERROR,
v.
JONATHAN HUDDLESON.
Supreme Court of United States.

*296 It was argued by Mr. Price and Mr. Nelson, for the plaintiff in error, and by Mr. Frick and Mr. McKaig, for the defendant in error.
Mr. Justice CURTIS delivered the opinion of the court.
This action was brought by the defendant in error, as superintendent of that part of the National Road lying within the State of Maryland, to recover a sum of money from the plaintiff in error, as the owner of stage-coaches passing over that road, and conveying passengers and the mails of the United States. The Court of Appeals for the Western Shore of the State of Maryland having rendered a final judgment in favor of the plaintiff, the defendant brought the case here by a writ of error, under the twenty-fifth section of the Judiciary Act.
The nature and extent of the compact between the United States and the several States of Ohio, Virginia, Maryland, and Pennsylvania, touching the parts of the road lying within the limits of each of those States, having been much considered by this court in the cases of Searight v. Stokes, 3 How. 151, and Neil et al. v. The State of Ohio, Id. 720, it is only necessary to state some of the conclusions there arrived at, and apply them to the law of Maryland now in question.
In the second of those cases it was decided, that the State of Ohio could not change the tolls fixed by its act, which Congress assented to, so as to vary the relative position and privileges of mail-coaches, in regard to tolls, as prescribed by that act.
*297 This decision is equally applicable to the original act of Maryland, to which Congress gave its assent; and the first inquiry is, whether the subsequent act of Maryland, now in question, will bear that test. The second section of the law of Maryland, to which Congress gave its assent, imposed, among other tolls, the following: "For every chariot, coach, coachee, stage, wagon, phæton, chaise, or other carriage, with two horses and four wheels, twelve cents; for either of the carriages last mentioned, with four horses, eighteen cents." And, inasmuch as coaches conveying the mail were not subject to any toll, there was by this law a discrimination in favor of mail-coaches, their proprietors bearing none of the burden of supporting the road, while the proprietors of other four-horse coaches did bear a part of that burden. On the 10th of March, 1843, the General Assembly of Maryland passed the act now under consideration, the material provisions of which are as follows:
"An act to amend the act entitled a supplement to an act entitled an act for the preservation and repair of that part of the United States road within the limits of the State of Maryland.
"Sec. 1. Be it enacted, by the General Assembly of Maryland, that from and after the passage of this act there shall be demanded and received by the toll-collectors on that part of the United States road, within the limits of the State of Maryland, from the owner or owners of every passenger or mail-coach or stage passing the gates on said road, the sum of four cents for every passenger carried in the same, for every space of ten miles on said road, and so in proportion for every greater or less distance, which shall be taken and received in lieu of the tolls now established by law on all coaches or stages with four horses passing over said road, and which shall be collected, paid out, and expended, as other tolls on said road are collected, paid out, and expended, under existing laws.
"Sec. 2. And be it enacted, That it shall be the duty of the proprietor, or proprietors, his her, or their agent, to furnish under oath, on the first Monday of every month, to the gate-keeper at number one, a list showing the number of passengers transported over said road in their respective coaches, for the month next preceding the time when said list is so returned.
"Sec. 3. And be it enacted, That, in the event of said proprietors or agents failing or refusing to comply with the provisions of the second section of this act, then, and in that case, it shall be the duty of the gate-keeper, at gate number one, to demand of, and receive from, such proprietor or proprietors so failing, the sum of one dollar for each and every stage-coach passing over said road its entire length."
*298 The discrimination which, under the original law, was made in favor of the proprietors of mail-coaches using the road, is not only destroyed by this law, but all toll is removed from the proprietors of other four-horse coaches, and a toll is imposed upon the proprietors of mail-coaches. It was held in both the former decisions, that the stipulation in the compact, that the United States should not thereafter be subject to any expense to maintain the road, was inconsistent with the imposition of a tax upon the contractors for carrying the mail in four-horse coaches, because the United States, requiring the mail to be so carried, would thus indirectly be made, through the enhancement of the price for this service, to bear a part of that burden. The effect of this law of Maryland is, therefore, to impose upon the United States, through the contractors for carrying the mail in four-horse coaches, a tax for the support of the road. It is argued that it is a tax upon the passengers, and not within the former decisions. But we do not so consider it. It is true, if he were to carry no passengers, and make the required returns of that fact, the proprietor would not be liable under this law to pay any toll. But the regulations of the Post-Office Department require him to take passengers for the security of the mail. If he carry the mail, he must also be a carrier of passengers; and this law would not have imposed a toll dependent upon the carriage of passengers in mail-coaches, unless it considered they would be carried. The real effect and meaning of the law is, therefore, to impose a tax on the proprietor of a four-horse coach which carries the mail, making the amount of that tax depend on the number of passengers carried. Now, the objection is not to the amount, but to the existence of the tax. Not having the power to impose any tax, it is no answer to say, its amount is regulated by the number of passengers.
This action is brought under the third section of the act to recover from the proprietor of mail-coaches the sum of one dollar for every mail stage-coach passing over the road. It is contended this is not a toll, but a penalty, for not complying with the directions contained in the second section of the act, to make returns. We think it more properly a commutation as to amount, for the tolls payable under the first section. It fixes their amount by operation of law, and without regard to the number of passengers carried; and is certainly subject to difficulties quite as great as would attend a demand for the tolls, under the first section.
Our opinion is, that, by reason of the compact between the United States and the State of Maryland, the tolls sued for could not be legally demanded, and that the decision of the Court of Appeals was erroneous and must be reversed.


*299 Order.
This cause came on to be heard on the transcript of the record, from the Court of Appeals of the Western Shore of the State of Maryland, and was argued by counsel. On consideration whereof, it is now here ordered and adjudged by this court, that the judgment of the said Court of Appeals in this cause be, and the same is hereby, reversed, with costs; and that this cause be, and the same is hereby, remanded to the said Court of Appeals, in order that such further proceedings may be had therein, in conformity to the opinion of this court, as to law and justice may appertain.
