On the 15th day of March, 1889, a number of railway companies (Ds) entered into an agreement by which they formed themselves into an Association to be known as the 'Trans-Missouri Freight Association, (D)' and they agreed to be governed by the provisions contained in the articles of agreement. The sole purpose behind D was to fix railroad rates. The agreement entered into between the railway companies stated, among other things, as follows: 'For the purpose of mutual protection by establishing and maintaining reasonable rates, rules and regulations on all freight traffic, both through and local, the subscribers do hereby form an association to be known as the Trans-Missouri Freight Association, and agree to be governed by the following provisions.' D had a chairman to investigate violations of the agreement and a committee was appointed to establish rates and rules for meeting competition of outside railroads. P sued under the Sherman Act claiming the agreement was simply a restraint of competition. D moved to dismiss in that its rates were reasonable and the agreement was not unlawful under the common law or under the Sherman Act. D got the motion and P appealed and the Court of Appeals affirmed. The Supreme Court granted certiorari.