Historian Nancy Seasholes gives us the first complete account of when, why, and how Boston's land was created. Fully one-sixth of Boston is built on made land. Although other waterfront cities also have substantial areas that are built on fill, Boston probably has more than any city in North America. Seasholes introduces findings from recent archeological investigations in Boston and relates landmaking to the major historical developments that shaped it. At the beginning of the 19th century, landmaking in Boston was spurred by the rapid growth that resulted from the burgeoning China Trade. The influx of Irish immigrants in the mid-19th century prompted several large projects to create residential land (not for the Irish, but to keep the taxpaying Yankees from fleeing to the suburbs). Many landmaking projects were undertaken to cover tidal flats that had been polluted by raw sewage discharged directly on them, removing the "pestilential exhalations" thought to cause illness. Land also was added for port developments, public parks, and transportation facilities, including the largest landmaking project of all, the airport.