Portland stone was used to create several important structures, including The Palace of Westminster (1347), The Tower of London (1349), and even elements of Buckingham Palace (1854). Portland stone has even found its way over the Atlantic, where it was utilized to construct the United Nations Headquarters in New York. This makes it the most popular material for government buildings. Buckingham Palace is a landmark building located in London, England. It is the largest residential palace in the world after the Kremlin in Moscow. Construction on the current version of Buckingham Palace began in 1714 for King George II. The original structure was designed by Robert Adam and built using materials such as Kentish ragstone and Italian marble. In 1837, under the direction of Charles Barry, the existing building was extensively modified and expanded to provide more living space for the growing royal family. Additional changes have been made since then, most notably the addition of the Gold State Dining Room in 2000. The palace stands within the grounds of the Royal Estate and is accessible through multiple entrances around the perimeter of the property. Visitors can arrive at the front door or from any of the upper-floor windows on the north side of the building. All major roads leading up to the palace are lined with trees that were brought in from all over Europe to beautify the approach. These include giant sequoia trees, red oak trees, and horse chestnuts among others.