Launceston had always been of strategic importance, situated on high ground that falls away steeply on two sides and with the River Kensey to the north. The castle was built by the Normans to suppress a Saxon uprising in 1068.

The count referred to was Robert of Mortain, half-brother of William the Conqueror. Robert's services were rewarded with vast estates in Cornwall, with him taking residence at Launceston in 1076.

The castle passed out of the Mortain family in 1106, through forfeiture to the Crown following the failure of a rebellion by Robert's son against William II. In 1141, the Earldom was appointed to Reginald de Dunstanville, one of Henry I's many illegitimate offspring, who held it until 1175.

The castle was then granted to John by his brother, Richard I, but was again returned to the Crown following another rebellion in 1191. During the next years, the castle underwent many rebuilds and refortifications.

During the early 1200s, there was no Earl of Cornwall, but in 1227, Henry III granted the earldom to his brother Richard, who stayed in command until 1272. Richard altered the castle again and rebuilt the entire town. At this time, the High Tower was added to the interior of the Keep and both gatehouses redesigned and moved. When Richard died in 1272, his son Edmund shifted the earldom's administration to Lostwithiel, and because of this movement of power, buildings at Launceston fell into disuse until the accession of Edward, The Black Prince, as the first Duke of Cornwall in 1337. Repairs to the dilapidated areas began in 1341 with the re-roofing of the Great Hall.

The castle was then used continually until John Leland's visit in 1539, when he specifically mentioned the Great Hall and chapel in his writings. The Hall stayed in use until the end of Elizabeth's reign, but by 1650, both it and the chapel were no longer in existence.

During the Civil War, the castle was held for the king except for two occasions in 1642 and 1644, when it was occupied by Parliamentarians. By 1650, however, the only occupied part of the castle was the north gatehouse. The extent to which the castle had fallen into ruin was amply demonstrated by the fact that the usual practise of dismantling the buildings was not deemed necessary.

The castle prison was bought by the county for use as the town gaol shortly afterwards. Hangings were performed in the bailey until 1821, but the gaol was demolished in 1842 after the assizes had moved to Bodmin

Following these events, the castle was used as a public park after its acquisition by the Duke of Northumberland, although the landscaping he performed destroyed much of the old castle. In 1951, it was transferred to the Ministry of Works and, in 1984, to the care of English Heritage.

Inside were two rooms, on top of one another, supported by wooden joists, the holes for which are still clearly visible, as is the grand fireplace in the upper room. The staircase first stops at an inner balcony, from where originally you would have entered the topmost room, then proceeds up again to where the battlements would have been.

This top room was known as the Earl’s Chamber and was well lit by a large vaulted window. It did not possess a latrine and was a long way from the kitchen in the bailey. It seems likely, therefore, that this chamber was used for formal entertainment rather than on a day-to-day basis. A further door in this room led out to the flat roof, formed with wooden beams laid between the tower and the top of the "outer" keep to form the fighting platform.

The view from the top is spectacular, and as such, the High Tower's primary role was that of a lookout post rather than an inner sanctum at time of siege.

Looking out from the very top, it is possible to see the line of relatively recent cottages built along the edge of the old town walls, as well as the ancient St Stephen’s church across the valley, which is where the major settlement was prior to the Norman invasion. All around are the fields and woods that at one time would have comprised the earl’s hunting park that stretched away towards Bodmin Moor.

The approach to the motte was by way of a wooden bridge over a deep ditch, defences put in place by Richard of Cornwall. The ditch separated the motte from the bailey with either end of the ditch enclosed by the curtain wall. Although the ancient bridge has long since disappeared, the modern replacement is supported by medieval piers and abutments.

The motte was constructed using earth, which was then packed down with heavy clays. Evidence also suggests that any spoil from improvements within the castle would also be thrown onto the mound to bolster its size and presence.

A 13th-century tower guarded the motte end of the bridge, as well as the stone stairway up the side to the keep, to the side of which is the well.

After a steep climb, you arrive at the keep. Initially this would have been a circular stone turret used as a fighting platform, protected further by a huge portcullis and earlier massive doors built into its walls, shored from the inside by wooden stakes wedged against them. Indeed, you can clearly see the sockets on the outer wall of the High Tower that accommodated these stakes. The top of the keep would have been covered in wooden roofing to provide a base to defend the structure.

Inside the keep was everything required to withstand a repeated assault: sleeping quarters, store rooms, and even a latrine that was flushed with clean water and exited via a chute to a drain on the outside floor of the keep.

At a later date, the High Tower was added.

Again, as with the southern entrance, it featured a long passage sealed with a portcullis and at least one set of massive doors, the hinges for which are still to be seen. There is a small room to the inside of the passage that would have housed the porter who controlled the gates, and beyond his quarters was a prison that continued to be used long after the castle ceased to have any military importance.

In 1656, George Fox, founder of the Quakers, was imprisoned here for 8 months. By all accounts, he was arrested in the town for distributing religious pamphlets, and when brought before the magistrate, refused to remove his hat.

Above the doorway is a plaque that reads, "George Fox 1624-1691 was imprisoned here for eight months. With other Quakers, he suffered under unspeakable conditions in Dooms-Dale," this being the name with which Fox christened the "pit" into which he was incarcerated. This plaque was placed by the local Society of Friends in 1991 to mark the tercentenary of Fox’s death.

Above the gate passage were apartments resided in by the castle constable (the Earl’s senior resident official), although nothing remains now. The bailey ramparts were cut back to allow construction of the full gateway in the late 13th century to replace the original 12th-century gate, so what we see today is not the original site of this entrance.

As has the rest of the site, it is built with local shale with the windows and doorways constructed with Polyphant volcanic stone from a village of the same name a few miles away. Granite has been used in some areas, although the hardness of this stone precluded its use to a certain degree, as it was too difficult to cut and shape.

The initial construction took place in the 12th century, with major rebuilds occurring until the 1400s. The window above the archway was originally part of a first-floor room that was reached via an external stone staircase. The deep sockets above the archway on the inside of the gate show where the original supporting floor timbers were positioned.

Also visible are two deep slots on either side, evidence of the portcullis that protected the gatehouse and huge sockets that would have held the hefty wooden beam in place to reinforce the wooden doors.

This gateway had an extended passage that continued over the castle ditch by way of a fortified bridge (barbican) and then continued via the medieval roadway to where the local Victorian Guildhall now stands.

In the 13th century, Richard of Cornwall undertook extensive reconstruction to include the building of two solid drum towers, creating an imposing entrance.

Subsidence and modern building of roads has seen much of the original gateway fall into ruin, and very little is left of the original structure. The ditch and most of the barbican were destroyed in 1834, during the construction of a new road, something, of course, that could never be repeated today. Gradual landslips have also seen the height of the original gateway drop by almost 5 feet. Discreet underpinning has ensured that this will occur no more.