The U.S. Postal Service is marking the anniversary by releasing the first of several postage stamps to be released through 2015 to coincide with key moments in the war’s history.

The first two stamps (see above and below) depict the battle at Fort Sumter and the battle at Bull Run near Manassas, Va.

The Postal Service held a first-day-of-issue event Tuesday at Liberty Square in Charleston, S.C., within earshot of where the war began.

The Civil War led to several changes in American mail delivery. The then-U.S. Post Office Department permitted Union soldiers to write “Soldier’s Letter” on the envelope because it was difficult to locate postage. Once delivered, postage was collected from the recipient.

According to the USPS historian, in July 1863, postage rates were simplified and free home deliveries began in the nation’s largest cities. A year later, the postal money order system began, making it safer for soldiers to send money back home.

The Confederacy also established its own post office system in February 1861, and it quickly recruited southern men working in the Post Office Department in Washington. Many of them brought along copies of postal reports, maps and other supplies.

The United States banned exchange of mail between the North and South in August 1861, but many smugglers carried mail illegally across borders, according to USPS. Prisoner-of-war mail was exchanged at designed points under a flag-of-truce.

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