Edinburgh Castle is built high upon the basalt remains of a long extinct volcano, recent archaeological excavations have discovered evidence for a settlement of round houses on the rock dating back to the late Bronze Age (about 900BC). Although the Army can’t claim to have occupied the castle then, it certainly can claim to have played its part in the bloodshed and strife which followed the establishment of Edinburgh Castle as a Royal Residence in the 11^th century.

Although the Army’s role within the Castle is much reduced, it still plays a key part in its security and ceremonial duties. Every evening the resident battalion posts an armed guard on the castle draw bridge. The castle guard is responsible for the security of the castle out with of public opening hours. The guard are responsible for the Honours of Scotland, the Crown jewels & the stone of destiny which is housed in the Jewel room of the Palace block. They also offer armed security for the military personnel who are resident in the castle.

The Army has responsibility for 2 buildings in the castle, the New Barrack Block (new in 1774 that is) and the Governors house, which today operates as the Officers Mess. The Governor of the Castle has always been the head of the Army in Scotland. Located within the New Barrack Block is the Home Headquarters of the Royal Scots Dragoon Guards (Carabineers & Greys). The Home Headquarters provides an essential and permanent link between the Serving Regiment and its roots in Scotland, dealing with recruiting, the Regiment's domestic affairs and coordinating the branches of the Regimental Association.  Home Headquarters also looks after the Regimental Archives, Museum and Shop. The Regimental Museum has moved to a new location within the Barrack Block after a £1.3million redevelopment. It was opened by the Colonel of the Regiment, Her Majesty the Queen during the summer of 2006.

 The One O’clock Gun is fired every day (except Sunday) at precisely 13:00, allowing citizens and visitors to check their clocks and watches.

The origin of the tradition lies in the days when sailing ships in the Firth of Forth were able to check and reset their chronometers in the days before accurate timepieces were available.

In 1861 Captain Wauchope, a Scottish Naval Officer in the Royal Navy invented the time ball, still seen today on Nelson's Monument on Calton Hill. At one O'clock the ball drops giving the signal to sailors. But this meant that someone would have to be watching at the time and it couldn't always be seen on foggy days. So, in the same year a cannon was fired from the Half Moon Battery at the same time the ball drops at the Nelson Monument. The gun could be easily heard by ships in Leith Harbour (2 miles away) The cannon was replaced with a 25 pound Howitzer in 1953 and has is now fired form Mill's Mount Battery on the North face of the Castle overlooking Princes Street Gardens.

During that time the medieval castle was transformed into a garrison fortress, and much of what the visitor sees today dates from this period.

The last military action the castle saw was during the 1745 Jacobite Rising when Bonnie Prince Charlie failed to take the fortress.

Over the next century the castle was used to hold prisoners of war during several conflicts including the Seven Years' War (1757-63), the War of American Independence (1775-83), and the Napoleonic wars
 (1793-1815). In 1923 the main garrison finally marched out to their new home, Redford Barracks, which is located to the south of the city.

Located in the old Provost Marshals house above the military prisons is the Regimental Home HQ of the Royal Scots. The Royal Scots (The Royal Regiment) are the oldest infantry regiment of the line in the British Army, being raised in 1633 during the reign of Charles 1^st. The regimental museum is also housed in the Castle, situated on the site of the old Governors stables opposite the New Barrack Block.