The practice of conferring orders originates with the mediaeval fraternities of knighthood, some of which still exist and are still awarded. While most modern orders have no roots in knighthood, they still tend to carry over the terms of their historic counterparts, and terms such as knight, commander, officer, members, and so on are still commonly found as ranks. A military order may use a medal as its insignia, however, most tend to have a unique badge or a type of plaque specifically designed for an emblem. The Medal of Honor is the highest military decoration awarded by the United States Government, and is an example of a decoration that is modeled as a military order, even though not expressly defining itself as one. It is bestowed on a member of the United States Armed Forces who distinguishes himself, "conspicuously by gallantry and intrepidity at the risk of his life above and beyond the call of duty while engaged in an action against an enemy of the United States." Each of the three departments of the American armed forces has a unique picture displayed on a medal, which is in turn displayed upon a star-shaped heraldic badge. The medal of the U.S. Army depicts the head of Minerva, the U.S. Navy medal shows a scene of Minerva doing battle with Discord, and the U.S. Air Force depicts the Statue of Liberty upon its medal. Military decorations, including medals and orders, are usually presented to the recipient in a formal ceremony. Medals are normally worn on more formal occasions and are suspended from a ribbon of the medal's colours on the left breast, while a corresponding ribbon bar is to be worn to common events where medals would be inappropriate or impractical to wear. Medallion is a vague term, often used for larger, usually circular, medals, which might be worn as pendants round the neck. It is the correct term for such medals from the late Roman Empire, typically distributed by the emperor and bearing his image, but in later periods larger medals are best termed just as medals. Generally circular, table medals are issued for artistic, commemoration, or souvenir purposes, not for commerce, and are too large to be plausibly worn. Tokens and Table Medals of coin-like appearance are part of the Exonumia subcategory of Numismatics, while Orders, Decorations, and Medals are considered Militaria (military related). The Nobel Foundation, the organization awarding the prestigious Nobel Prize, presents each winner, "an assignment for the amount of the prize, a diploma, and a gold medal..."