While Manhattan's streets were largely laid out with the Commissioners' Plan of 1811, this grid system was only implemented between Houston and 155th Streets. The plan left Greenwich Village with its long-established mews, alleys, and courts, many of which date to the city's early colonial period, intact. While not exclusively in the Village, most of the secret streets on this list are located there among the organically developed 18th-century street plan. While some changes have come to these streetscapes in the last century, in most cases their concealment and a healthy dose of historic preservation work have aided in their continued survival in the 21st century.