The pitcher's mound is a low artificial hill found in the center of a baseball diamond. On the mound there is a white rubber slab, called the pitcher's plate or commonly the rubber, six inches (15 cm) front-to-back and two feet (61 cm) across, the front of which is exactly sixty feet six inches (18.4 m) from the rear point of home plate. This peculiar distance was set by the rulemakers in 1893, not due to a clerical or surveying error as popular myth has it, but purposely (as noted below).
In Major League Baseball, a regulation mound is 18 feet (5.5 m) in diameter, with the center 59 feet (18.0 m) from the rear point of home plate, on the line between home plate and second base. The front edge of the pitcher's plate or rubber is 18 inches (45.7 cm) behind the center of the mound, making the front edge's midpoint 60 feet 6 inches (18.4 m) from the rear point of home plate. Six inches (15.2 cm) in front of the pitcher's rubber the mound begins to slope downward. The top of the rubber is to be no higher than ten inches (25.4 cm) above home plate. From 1903 through 1968 this height limit was set at 15 inches, but was often slightly higher, sometimes as high as 20 inches (50.8 cm), especially for teams that emphasized pitching, such as the Los Angeles Dodgers, who were reputed to have the highest mound in the majors.
A pitcher will push off the rubber with his foot in order to gain velocity toward home plate when pitching. In addition, a higher mound generally favors the pitcher over a lower mound. With the height advantage, the pitcher gains more leverage and can put more downward velocity on the ball, making it more difficult for the batter to strike the ball squarely with the bat. The lowering of the mound in 1969 was intended to "increase the batting" once again, as pitching had become increasingly dominant, reaching its peak the prior year; 1968 is known among baseball historians as "The Year of the Pitcher". This restrictive rule apparently did its job, contributing to the hitting surge of modern baseball.
In Little League Baseball, the distance between the mound and homeplate is 46'. On "Pony" fields, homeplate is usually located about 54' away. This adjustment each graduation between leagues prepares the youngster for the maximum distance of 60 feet 6 inches in high school baseball.
A pitcher's mound is difficult for groundskeepers to maintain. On youth and amateur baseball fields, the mound may be much different from the rulebook definition due to erosion and repair attempts. Even in the major leagues, each mound gains its own character, as pitchers are allowed to kick away pieces of dirt in their way, thereby sculpting the mound a bit to their preference.