Book excerpt: When the Boston Elevated Railway Company broke ground for the Cambridge Subway in May 1909, its intention was to provide the cities of Boston and Cambridge with the finest and most efficient rapid-transit system of the time. Other cities, such as New York and Philadelphia, paid close attention, adopting many of the Cambridge Subway's revolutionary design features. The subway became known as the Red Line and eventually extended from Cambridge across the Charles River through Boston, serving Dorchester, Braintree, and Mattapan. Boston's Red Line: Bridging the Charles from Alewife to Braintree details one of Boston's oldest and busiest subway lines. This nostalgic collection of vintage photographs documents the line's construction and its engineers and leaders, such as Maj. Gen. William A. Bancroft, mayor of Cambridge and president of the Boston Elevated Railway Company. In these pages, watch as crews break ground in Harvard and Andrew Squares and see the 1929 trolleys that replaced Mattapan's commuter train service. Through exciting, historic photographs, Boston's Red Line: Bridging the Charles from Alewife to Braintree tells the fascinating story of how the Crimson City's subway became the modern Red Line, taking passengers beneath the streets of Boston to landmarks such as Harvard Square, Massachusetts General Hospital, historic Park Street, and the Longfellow Bridge.