|By the late 1840s, the marshland west of the Public Garden had become so polluted it was considered a health hazard, and officials had no choice but to act. The solution was to fill in the quagmire, in a land reclamation project that would double the size of the original Boston peninsula. The project began in 1858 and finished in 1882. This 1860 map illustrates proposed streets of the Back Bay. The area was designed as a grid with Commonwealth Avenue as the central boulevard of five east-west corridors, and eight north-south cross streets named for English nobility.