▁to ▁enc lose ▁the ▁Back ▁Bay ▁bas in ▁and ▁util ize ▁the ▁flow ing ▁tid al ▁waters ▁for ▁industrial ▁production . ▁Con struct ing ▁the ▁dam ▁would ▁allow ▁water ▁to ▁reli ably ▁flow ▁from ▁the ▁Charles ▁River ▁to ▁the ▁bas in , ▁creating ▁an ▁ideal ▁environment ▁for ▁the ▁era ' s ▁industrial ▁mill s . ▁The ▁project ▁addition ally ▁added ▁a ▁second ▁route ▁to ▁the ▁main land ▁that ▁redirect ed ▁traffic ▁away ▁from ▁Boston ' s ▁ch oked ▁Orange ▁Street ▁cause way . ▁ ▁Between ▁ 1 8 1 8 ▁and ▁ 1 8 2 1 , ▁the ▁dam ▁was ▁constructed ▁by ▁extending ▁Be acon ▁Street ▁west ward . ▁ ▁Geography ▁▁ ▁The ▁Boston ▁Mil ld am ▁occupied ▁what ▁is ▁today ▁the ▁west ward ▁extension ▁of ▁Be acon ▁Street . ▁Prior ▁to ▁the ▁construction ▁of ▁the ▁Mil ld am , ▁Be acon ▁street ▁ended ▁at ▁the ▁foot ▁of ▁Charles ▁Street ▁– ▁Back ▁Bay ' s ▁tid al ▁bas in ▁prevent ed ▁any ▁further ▁construction . ▁The ▁dam ▁had ▁two ▁arms , ▁one ▁stretch ing ▁from ▁Be acon ▁Hill ▁to ▁S ew all ' s ▁point ▁( today , ▁Ken more ▁Square ) ▁and ▁one ▁stretch ing ▁from ▁Ro x bury ' s ▁Gra vel ly ▁point . ▁These ▁sections ▁of ▁the ▁dam ▁en closed ▁the ▁back ▁bay ▁in ▁a ▁ 6 0 0 - acre ▁tid al ▁bas in . ▁The ▁tid al ▁bas in ▁was ▁later ▁filled ▁in ▁and ▁is ▁now ▁occupied ▁by ▁the ▁Back ▁Bay ▁Ne igh bor hood . ▁