hornwork, was located here. The present Esplanade was laid out as a parade ground in 1753, and extended in 1845. It is upon this Esplanade that the Edinburgh Military Tattoo takes place annually. From the Esplanade the Half Moon Battery is prominent, with the Royal Palace to its left. The Gatehouse at the head of the Esplanade was built as an architecturally cosmetic addition to the castle in 1888. Statues of Robert the Bruce by Thomas Clapperton and William Wallace by Alexander Carrick were added in 1929, and the Latin motto Nemo me impune lacessit is inscribed above the gate. The dry ditch in front of the entrance was completed in its present form in 1742. Within the Gatehouse are offices, and to the north is the most recent addition to the castle; the ticket office, completed in 2008 to a design by Gareth Hoskins Architects. The road, built by James III in 1464 for the transport of cannon, leads upward and around to the north of the Half Moon Battery and the Forewall Battery, to the Portcullis Gate. In 1990, an alternative access was opened by digging a tunnel from the north of the esplanade to the north-west part of the castle, separating visitor traffic from service traffic. Portcullis Gate and Argyle Tower The Portcullis Gate was begun by the Regent Morton after the Lang Siege of 1571–73 to replace the round Constable's Tower, which was destroyed in the siege. In 1584 the upper parts of the Gatehouse were completed by William Schaw, and these were further modified in 1750. In 1886–1887 this plain building was replaced with a Scots Baronial tower, designed by the architect Hippolyte Blanc, although the original Portcullis Gate remains below. The new structure was named the Argyle Tower, from the fact that the 9th Earl of Argyll had been held here prior to his execution in 1685. Described as "restoration in an extreme form", the rebuilding of the Argyle Tower was the first in a series of works funded by the publisher William Nelson. Just inside the gate is the Argyle Battery overlooking Princes Street, with Mills Mount Battery, the location of the One O'Clock Gun, to the west. Below these is the Low Defence, while at the base of the rock is the ruined Wellhouse Tower, built in 1362 to guard St. Margaret's Well. This natural spring provided an important secondary source of