<P> Part of the original ballpark construction of 1912, the wall is made of wood, but was covered in tin and concrete in 1934 when the scoreboard was added . The wall was covered in hard plastic in 1976 . The scoreboard is manually updated throughout the game . Despite the name, the Green Monster was not painted green until 1947; before that it was covered with advertisements . The Monster designation is relatively new; for most of its history it was simply called "the wall ." In 2003, terrace - style seating was added on top of the wall . </P> <P> "The Triangle" is a region of center field where the walls form a triangle whose far corner is 420 feet (130 m) from home plate . That deep right - center point is conventionally given as the center field distance . The true center is unmarked, 390 feet (120 m) from home plate, to the left of "The Triangle" when viewed from home plate . </P> <P> There was once a smaller "triangle" at the left end of the bleachers in center field, posted as 388 feet (118 m). The end of the bleachers form a right angle with the Green Monster and the flagpole stands within that little triangle . That is not the true power alley, but deep left - center . The true power alley distance is not posted . The foul line intersects with the Green Monster at nearly a right angle, so the power alley could be estimated at 336 feet (102 m), assuming the power alley is 22.5 ° away from the foul line as measured from home plate . </P> <P> "Williamsburg" was the name, invented by sportswriters, for the bullpen area built in front of the right - center field bleachers in 1940 . It was built there primarily for the benefit of Ted Williams, to enable him and other left - handed batters to hit more home runs, since it was 23 feet (7.0 m) closer than the bleacher wall . </P>

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