The Baltimore & Ohio (B&O) Railroad was chartered by the Maryland State Legislature in February 1827. The initial objective for the B&O was to link Baltimore with the Ohio River and thus facilitate trade between the eastern states (via Baltimore) and the interior reaches of the western US. It was conceived in response to the commercial success being enjoyed by the Erie Canal (in New York) and the potential dilution of trade in and out of Baltimore that it could cause.
Construction on the B&O formally began in the summer of 1828. The railroad originally stretched from Baltimore west into Virginia (later West Virginia), crossed the Allegheny Mountains and eventually met the Ohio River outside of Moundsville, Virginia (later West Virginia) in December 1852 - more than two decades after construction began!
The B&O was the first "common carrier" railroad in the United States; it was chartered by the Maryland Legislature to serve the public via the transport of passengers and freight.
In 1927, in recognition of its centennial, the Baltimore & Ohio Railroad Company decided to celebrate with a gala dinner in February to mark its charter anniversary, plus stage a Centenary Exhibition and Pageant - "The Fair of the Iron Horse"- later in the year (September/October). The Exhibition was staged at Halethorpe (southwest of Baltimore) on approximately 1,000 acres owned by the B&O Railroad; the property was adjacent ot the rail line.
The exhibition and its displays were designed to tell the history/story of inland transportation with a focus on the B&O's role; the Exhibition did include horse-drawn carriers and canal boats to help provide a more complete picture. A parade (staged daily at the Exhibition and Pageant site) was held and an Exhibition book was created. B&O also commissioned a very attractive (IMO) commemorative medal!
The Exhibition and Pageant was a significant event, with an estimated 25,000+ people in attendance for its opening. B&O President Daniel Willard opened the event with a brief welcoming speech, and was followed by a brief address from Maryland Governor Albert Ritchie. Presidents and other officers of domestic and international railroad companies were present, as were Secretary of Commerce Herbert Hoover, Secretary of the Interior Hubert Work and Attorney General John G. Sargent of President Calvin Coolidge's cabinet; Coolidge was not present.
B&O President Willard, in his brief opening remarks, commented, "One hundred years ago this very year a small group of Baltimore businessmen decided to build a railroad from Baltimore to the Ohio River for general transportation purposes. A charter was secured from the Maryland Legislature, a company was organized, money was raised and construction was begun. The Baltimore & Ohio Railroad, as we know it today. is the result of that beginning, plus the continuous growth of 100 years."
The Exhibition/Fair was a large success, attracting more than 1,225,000 visitors during the three weeks it was open (September 24 - October 15, 1927).
The commemorative medal (2-3/4" in diameter) was given to the approximately 1,000 guests at the B&O's February anniversary dinner. The medal was struck in bronze by the Medallic Art Company of New York; it was designed by Hans Schuler of Baltimore. Schuler also designed the commemorative half dollar and official medal of the 1934 Maryland Tercentenary.
As the information card (shown below) presents good descriptions of the medal's obverse and reverse designs, I won't repeat the descriptions here.
1927 Baltimore & Ohio Railroad Centennial Medal
1927 Baltimore & Ohio Railroad Centennial Medal - Description Card
1927 Baltimore & Ohio Railroad Centennial Medal - Presentation Card
1927 Baltimore & Ohio Railroad Centennial Medal - Presentation Case 
I'm glad I was able to add a "complete" B&O Railroad medal to my collection. The example I purchased includes the original Description Card and personalized Presentation Card along with the medal's original navy blue Presentation Case.
Sadly, this icon of American history (and one of four railroads available on the Monopoly (r) board) no longer exists. It was merged into the Chesapeake and Ohio Railroad under the CSX Corporation umbrella in 1987.
For other of my posts about commemorative coins and medals, check out:
Read More: Commems Collection.