The last time MLB made a major rule change for the Pitchers’ mound was 1969. In 1904 the height of the mound was limited to no more than15 inches higher than the level of the baselines and pitchers were prohibited from soiling a new ball.
In reaction to the complete dominance of pitching over hitting in 1968, MLB attempted to recalibrate the balance to favor the hitters by lowering the mound 5 inches to a height of 10” inches above baseline.
This was one change that was part of a general policy to make the game more exciting for fans by increasing the number of hits and runs scored, which later led to the intrusion of the DH rule in 1976.
Media consultants told MLB that only purists enjoyed shutouts and close, low-scoring games—“pitchers’ matches”—and that the majority of fans wanted to see more scoring and more HRs.
When the Steroid Era arrived and Mark McGwire and Sammy Sosa were “chasing the Babe,” Commissioner Bud Selig promoted the race and, since it was creating more fan interest and revenues for MLB, he continued to turn a blind eye to the readily apparent used of steroids.
Prior to the Steroid Scandal in MLB, most sudden changes in the delicate balance between the pitcher and the batter was attributed to “juiced” baseballs, “corked” bats, and the height of the mound.
Before the pitcher’s mound was introduced in 1893, there was a 4 foot wide by 5 1/2 foot long box on flat ground; the pitcher could put his back foot anywhere along the 4 foot back line of the box, which was 55 1/2 feet from home plate, to start his pitch.
In 1893, to create more offense, the box was replaced with a raised mound and a rubber slab 12 inches long and relocated further back to 60 1/2 feet from home plate. Pitches were required to be touching with their back foot and the rubber plate was 60 1/2 feet away from home plate.
The extra five feet was significant, as it cut down on the angle of the pitches and the league batting average spiked up 35 pts. in 1893 and another 29 pts. in 1894.
Until 1950, MLB only required that the height of the mound be no more than 15” above the baseline, but did not address a minimum height. This lack of interest in the state of the mound by MLB led to attempts to adjust the height from 0-15 inches to suit the style of individual home team pitchers, or work against the style of visiting pitchers.
"“Altering the height of the mound gradually developed into an art form.” "
“As a means of utilizing to the full the blinding side-arm speed of Walter Johnson, Washington leveled off the ‘mound’ so completely that it was almost a depression instead of an elevation.” 
The great baseball man and creative impresario, Bill Veeck, while he was GM at Cleveland, had Emil Bossard, “the Michelangelo of grounds keepers,” who custom crafted the Indians’ mound to the preferences of the pitcher of the day. 
“Bob Feller always liked to pitch from a mountaintop, so that he could come down with that great leverage of his and stuff the ball down the batter’s throat.” 
All this chicanery was perfectly legal in MLB, prior to 1950, when a rule required all mounds to be the same height—exactly than 15” above the baseline, no less.
With the growing use of relief pitchers, a mound that was customized for the starter did not always suit the home team’s subsequent hurlers:
“Bob Turley wanted the mound at Yankee Stadium to be flat and since he was the top gun of the staff in 1958, the grounds keepers kept it that way. ..I preferred it to be sloped…One day I threw my first pitch and my foot hit the ground and I thought my knee was going to hit me in the chin.” 
With the historic trend for pendulum swings in baseball rules, the height of the mound may someday be adjusted, downward, to enhance fan interest and increase the profits in MLB.
 Peter Morris, A Game of Inches, p. 482.
 Arthur Dailey, Inside Baseball, p. 61.
 Bill Veeck, Veeck—As in Wreck, p. 161.]
 Danny Peary, We Played The Game, p 420.]
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Gene Collier, Post-Gazette C. “SERMON ON THE MOUND.” Pittsburgh Post – Gazette: D.3. Apr 30, 1995 1995. Print.
Lee, Matthew. “The Average Speed of a Baseball.” LIVESTRONG.COM. Livestrong, 7 May 2011. Web. 27 Nov. 2012. .
Leggett, William. “From Mountain To Molehill.” Sports Illustrated 24 Mar. 1969: n. pag.When Baseball Decided to Lower the Pitching Mound to Help. Web. 27 Nov. 2012. .
News Staff. “Lower Pitcher’s Mound Will Reduce Baseball Injuries – Study.” Scientific Blogging. Scientific Blogging, 23 Mar. 2008. Web. 27 Nov. 2012. .
“Official Rules | MLB.com: Official Info.” Major League Baseball. MLB, n.d. Web. 27 Nov. 2012. .
Silverman, Steve. “How Far Is It From Home Plate to the Pitcher’s Mound in Major League Baseball?” LIVESTRONG.COM. Livestrong, 26 May 2011. Web. 27 Nov. 2012.