Few castles have a history as rich and as intertwined with the history of England as the Tower of London. This account can only be a brief summary of the history of the castle, but there are many books available that go into much greater depth, many of which are available from shops inside the castle.

By the end of the Anglo-Saxon period London had become the most powerful city in England. When William of Normandy defeated King Harold II at Hastings in 1066 one of his first priorities was to secure London. After receiving the submission of the English magnates at Little Berkhampstead, William sent an advance guard into London to construct a castle and prepare for his triumphal entry.

Initially the Tower consisted of a modest enclosure built into the southeast corner of the Roman City walls, but by the late 1070s, with the initial completion of the White Tower, it had become the most impressive castle in England. The White Tower was protected to the east and south by the old Roman City Walls, while the north and west sides were protected by ditches as much as 7.50m (25ft) wide and 3.40m (11ft) deep and an earthwork with a wooden wall on top. In the 12th century a 'forebuilding' (now demolished) was added to the south front of the White Tower to protect the entrance. From very early on the enclosure contained a number of timber buildings for residential and service use.

When Richard the Lionheart (1189-99) came to the throne he departed on a crusade to the Holy Land leaving his Chancellor, William Longchamp, Bishop of Ely, in charge of the Kingdom. Longchamp soon embarked on a series of building campaigns to enlarge and strengthen the Tower of London, and by 1350 had created the basic form of the castle as we see it today.

Longchamp's works doubled the area covered by the castle by digging a new deeper ditch to the north and east and building sections of the curtain wall, reinforced by a new tower (now known as the Bell Tower) at the southwest corner. The ditch was intended to flood naturally from the river, but this was not a success.

During the reign of King Henry III (1216-72) the Tower of London underwent further development. Starting with the expansion of the royal accommodation in the enclosure that formed the Inmost Ward. The great hall and kitchen, dating from the previous century, were improved and two towers were built on the waterfront, The Wakefield Tower as the King's lodgings and the Lanthorn Tower, probably intended as the queen's lodgings. A new wall was also built enclosing the west side of the Inmost Ward.

In 1238 Henry launched a new building programme with the construction of a great new curtain wall round the east, north and west sides of the castle. The new wall doubled the area covered by the fortress, enclosing the neighbouring church of St Peter ad Vincula. It was surrounded by a moat, this time successfully flooded by a Flemish engineer, John Le Fosser. The wall was reinforced by nine new towers, the strongest at the corners (the Salt, Martin and Devereux).

In 1272 King Edward I (1272-1307) came to the throne and continued the work begun by his father. The work included building the existing Beauchamp Tower, but the main effort was concentrated on filling in Henry III's moat and creating an additional curtain wall on all four sides and surrounding it with a new moat. This wall enclosed the existing curtain wall built by Henry III and was pierced by two new entrances, one from the land on the west, passing through the Middle and Byward towers, and another under St Thomas's Tower, from the river. New royal lodgings were included in the upper part of St Thomas's Tower.

King Edward II (1307-27) improved the walls put up by his father and moved the royal lodgings from the Wakefield Tower and St Thomas's Tower to the area round the present Lanthorn Tower. The old royal lodgings were now used for his courtiers and for the storage of official papers by the King's Wardrobe (a department of government that dealt with supplies). The use of the Tower for functions other than military and residential had been started by Edward I who put up a large new building to house the Royal Mint and began to use the castle as a place for storing records. As early as the reign of Henry III the castle had been regularly used as a prison. The Tower also served as a treasury (the Crown Jewels were moved from Westminster Abbey to the Tower in 1303) and as a showplace for the King's animals. In 1255 King Louis of France gave Henry III the first elephant seen in England, it was kept at the Tower in a specially built elephant house.

Edward III (1327-77) put up a new gatehouse between the Lanthorn Tower and the Salt Tower, together with the Cradle Tower and its postern (a small subsidiary entrance), a further postern behind the Byward Tower and another at the Develin Tower. He was also responsible for rebuilding the upper parts of the Bloody Tower and creating the vault over the gate passage and extending the Tower Wharf eastwards as far as St Tomas's Tower. This was completed in its present form by his successor Richard II (1377-99).

During the reign of Henry VI (1422-61 and 1470-71) England entered the period of civil disorder and political instability known as the Wars of the Roses. Throughout this period the Tower of London was a key asset to those who held the throne or wished to. In victory, Edward IV (1461-70 and 1471-83) held lavish courts there in 1465 and 1470; Richard III (1483-85) presided over celebrations for his coronation in 1483 and Henry VII (1485-1509) entertained his victorious supporters there after he had won the throne in 1485. For the defeated however the Tower was the scene of murder and execution; victims included Henry VI in 1471, the young Edward V and his brother (the Princes in the Tower) in 1483 and George, Duke of Clarence in 1478.

The first Tudor monarch, Henry VII (1485-1509), extended his own lodgings around the Lanthorn Tower adding a new private chamber, a library, a long gallery, and also laid out a garden. These buildings were to form the nucleus of a much larger scheme begun by his son, Henry VIII (1509-47), who put up a large range of timber-framed lodgings at the time of the coronation of his second wife, Anne Boleyn. The building of these lodgings, used only once, marked the end of the history of royal residence at the Tower.

The Tower took on an expanded role as the home for a large number of religious and political prisoners during the Tudor years, started by the Reformation (when Henry VIII broke with the Church in Rome).

Sir Thomas Moore and Bishop Fisher of Rochester were both executed in 1535 for refusing to acknowledge Henry VIII as head of the English Church. The King's second wife, Anne Boleyn, was executed along with her brother and four others a little under a year later. July 1540 saw the execution of Thomas Cromwell, Earl of Essex and former chief minister of the King. Two years later, Catherine Howard, the second of Henry VIII's six wives to be beheaded, was executed.

The reign of Edward VI (1547-53) saw a continuation of the political executions which had begun in his father's reign; the young King's protector, the Duke of Somerset, and his confederates met their death at the Tower in 1552, falsely accused of treason. During Edward's reign the English Church became more protestant, but the King's early death in 1553 left the country with a Catholic heir, Mary I (1553-58). During her brief reign many important Protestants and political rivals were either imprisoned or executed at the Tower. The most famous victim was Lady Jane Grey, and the most famous prisoner was the Queen's sister Princess Elizabeth (the future Elizabeth I). Religious controversy did not end with Mary's death in 1583; Queen Elizabeth I spent much of her reign warding off the threat from Catholic Europe. The Tower was kept full of prisoners, including bishops, archbishops, knights, barons, earls and dukes many of whom spent months, even years, languishing in the towers of the Tower of London.

In 1642, during the reign of Charles I (1625-49), civil war broke out between King and parliament. In 1643 the Tower was seized from the King by parliamentarians and remained in their hands throughout the Civil War (1642-49). During this time a permanent garrison was installed in the Tower for the first time, by Oliver Cromwell, soon to be Lord Protector but then a prominent parliamentary commander. The loss of the Tower, and London as a whole, was a crucial factor in the defeat of Charles I by Parliament.

The monarchy was restored in 1660 and the reign of the new King, Charles II (1660-85) saw further changes in the functions of the Tower. Its role as a state prison declined, and the Office of Ordnance (which provided military supplies and equipment) took over responsibility for most of the castle, making it their headquarters. During this period another long-standing tradition at the Tower began - the public display pf the Crown Jewels.

Under the control of the Office of Ordnance the Tower was filled with a series of munitions stores and workshops for the army and navy. The army also built new barracks to accommodate the expanding garrison.

Early in the 19th century many of the historic institutions that had been housed within the Tower's walls, began to move out. The first to go was the Mint in 1812, followed by the Royal Menagerie in 1834 which became the nucleus of what is now London Zoo. The Record Office moved to Chancery Lane in 1834 and, after the War Office assumed responsibility for the manufacture and storage of weapons in 1855, large areas of the fortress were vacated by the old Office of Ordnance.

The final period of refortification, in response to the Chartist movement of the 1840s (which sought major political reform), saw new loop-holes and gun emplacements built, along with the present Waterloo Barracks and the Royal Fusiliers' building and alterations to the Brick, Flint and Bowyer towers.

The vacation of large parts of the Tower by the offices which had formerly occupied it, and an increasing interest in the history and archaeology of the Tower, led, after 1850, to a programme of 're-medievalisation'. Many of the old Ordnance buildings, barracks and service buildings were cleared, while the old towers were restored to their medieval appearance.

The second half of the 19th century saw a great increase in the number of visitors to the Tower, although sightseers had been admitted as early as 1660. By the end of Queen Victoria's reign in 1901, half a million people were visiting the Tower each year.

The First World War (1914-18) left the Tower largely untouched, however the war brought the Tower of London back into use as a prison for the first time since the early 19th century when eleven spies were held and subsequently executed in the Tower. The last execution in the Tower took place in 1941 during the Second World War (1939-45). Bomb damage during the Second World War was much greater; a number of buildings were severely damaged or destroyed. During the Second World War the Moat, which had been drained and filled in 1843, was used as allotments for vegetable growing and the Crown Jewels were removed from the Tower and taken to a place of safety.

Today the Tower of London attracts 2.5 million visitors a year.

This history of the Tower of London was taken from the Tower of London Official Guidebook.