Located at the western end of the Stanegate, the Roman roadway that crossed northern England, the Cumbrian city of Carlisle has long been valued for its strategic value. In 1092, some 500 years after the Romans abandoned the post, the Normans established themselves at the site, which had been in Scottish hands since 1068. Recognizing the potency of the location - Scotland is a mere 10 miles away and the site stands on a bluff overlooking the River Eden - Carlisle was deemed the ideal place to erect a castle.

In the Middle Ages, Carlisle became a key forward outpost for England's monarchs during their long struggle against the Scots when the castle changed hands repeatedly from the 12th to the 18th century.. The Scottish King David I first took the castle in 1136, but lost it to Henry II. Alexander, King of the Scots, took it again in 1216 but lost it to Edward I of England who later staged his invasion of southern Scotland from the castle. Bonnie Prince Charlie was the last Scot to successfully take the castle, in a six day battle, but soon thereafter lost it again to the Duke of Cumberland.

Later, the castle became a depot for arms and ammunition and a barracks for the military, which remained there throughout the Second World War. Even though extensive modifications over the centuries have transformed the original stronghold into a powerful artillery fortress, the layout of the castle remains true to its medieval origins. A masonry cross-wall and ditch separate the site into inner and outer baileys and a stone curtain wall frames the entire complex.

A bailey is an enclosed courtyard, typically surrounded by a wooden fence, earthen or stone wall and overlooked by the motte. A castle could have more than one bailey, sometimes an inner surrounded by a lesser wall and an outer surrounded by a strong wall. The motte was a mound built in the center of the bailey with very thick walls (the last wall of defense), as great a height as was practicable in the form of a tower and in it was built the castle keep, itself the living quarters, etc.

A single gateway breached the wall's southern side, so visitors from the city could enter the castle. All in all, Carlisle is an outstanding example of a stone-enclosure castle. As early as the 12th century, Henry I began strengthening Carlisle Castle in stone and enclosing the city with masonry walls. He probably started work on the castle's oldest surviving structure, the Great Keep, in about 1122, but it was his successors who actually completed the massive stone rectangle. In its heyday the keep stood over 65 feet high. During the 18th century Jacobite Rising - an abortive attempt to place Bonnie Prince Charlie on the British throne - a first floor chamber served as a prison. Jacobite prisoners licked the stones of their cells, which were reputedly a source of moisture, to quench their thirst.

Besides the Great Keep, the inner guardhouse (known as the Captain's Tower), remnants of the royal apartments and other domestic buildings survive from the medieval period. Queen Mary'' Tower, named for its most famous prisoner, Mary, Queen of Scots, dates to the 14th century. It now holds the museum of the King's Own Royal Border Regiment.

During the 1540s, Henry VIII initiated the first of several major modernization projects to refit the castle for artillery. Over the course of the next 350 years, the ongoing presence of the army and the castle's continued use as a military depot and armory forced further alterations to the structure, as weapons technology evolved and the fortifications decayed.

Today the castle no longer fears the impact of battle and aging on its battlements. The sturdy red walls, which starkly contrast with the green fields at their base, stand as an everlasting reminder of the turmoil that plagued the borderland between England and Scotland. Nowadays Carlisle Castle is managed by English Heritage and is open for visitors throughout the year.