The Palmerston Forts that defend Dover were built in response to the 1859 Royal Commission dealing with the perceived threat of a French invasion. The forts were intended to defend the Port of Dover, that would provide direct access to an invasion fleet, from capture. Construction was carried out by the Royal Engineers and civilian contractors (under Royal Engineer supervision). In addition to the newly constructed forts, extensive work was carried out on existing fortifications. The fortifications built or upgraded as part of the works were: