There is reason to believe that an armed expedition is about to be fitted out in the United States with an intention to invade the Island of Cuba of some of the Provinces of Mexico. The best information which the Executive has been able to obtain points to the Island of Cuba as the object of this expedition. It is the duty of this Government to observe the faith of treaties and to prevent any aggression by our citizens upon the territories of friendly nations. I have, therefore, thought it necessary and proper to issue this Proclamation, to warn all citizens of the United States who shall connect themselves with an enterprise so grossly in violation of our laws and out treaty obligations that they will thereby subject themselves to the heavy penalties denounced against them by our Acts of Congress, and will forfeit their claim to the protection of their country. No such person must expect the interference of this Government in any form on their behalf, no matter to what extremities that may be reduced in consequences of their conduct. An enterprise to invade the territories of a friendly nation, set on foot and prosecuted withing the limits of the United States, is in the highest degree criminal, as tending to endanger the peace and compromit the honor of this nation; and therefore, I exhort all good citizens, as they regard our national reputation, as they respect their own laws and the laws of nations, as they value the blessings of peace and the welfare of their country, to discountenance and prevent by all lawful means any such enterprise; and I call upon every officer of this Government, civil, or military, to use all efforts in his power to arrest for trial and punishment every such offender against obligations to friendly Powers.

Given under my had, the eleventh day of August, in the year of our Lord one thousand eight hundred and forty-nine, and the seventy-fourth of the independence of the United States.

                                                                                                                                                        Z. Taylor
By the President:
J. M. Clayton, Secretary of State

The Proclamation, a copy of which will be found in another column, was received yesterday at the Department of State, in a communication from the President of the United States, at Harrisburg, Pennsylvania.

For some weeks past the country has been disturbed with rumors of the assembling and drilling of bands of men in different parts of the United States. Various places have been artfully designated as the object of their destination. Tampico and the Sierra Madre Provinces of Mexico, Yucatan and Cuba, have all been alluded to in connexion with the enterprise. But the truth has been studiously concealed by the leaders engaged in it. The common soldiers who have been enlisted were not to be entrusted with the secret as to the object to be effected until after embarkation. How far the expedition has proceeded we know not. But we do know that bands of men have lately assembled at a point not far from New Orleans; and that the evidence is clear that Cuba is the real object of those engaged in it. Most earnestly do we hope that the President may succeed in arresting the perpetration of such an outrage on a friendly nation, and maintaining unsullied the honor of our country. Plunder can be the only motive of such an enterprise; and all good men must rejoice to witness the honest redemption of General Taylor's pledges to his country, to preserve the faith of our treaties and suppress all illegal enterprises against friendly foreign nations. The gallant soldier who has spend forty years in the camp, and braved the bullets of his country's enemies in so many battles-who has sounded all the shoals and depths of military glory-proves himself to the world to be, as we predicted before his election that he would be, the "Man of Peace."