It's the oldest and biggest occupied castle in the world that has been home to 39 monarchs. And it will shortly play host to Prince Harry and Meghan Markle's wedding.
However, the story of Windsor Castle begins with a wooden fortress, built by William the Conqueror in the 11th century.
In the decade after the Norman invasion of 1066, he had it constructed to guard the Thames Valley. Today, all that remains of this structure is the mound on which the castle's iconic Round Tower stands.
Over the years, the castle grew considerably, with notable changes including vineyards planted by Henry II in the 12th century, and Elizabeth I's long gallery, built in 1583 for the Queen to take walks in bad weather.
Now, archaeologists and researchers have calculated that the original 'Windsor' was just a fifth of its present size.
Their findings are revealed in a new book - Windsor Castle: A Thousand Years of a Royal Palace - complete with artist's impressions of what the site would have looked like in its early days.
Based on the evidence of new research, historic manuscripts, drawings and paintings, and recent GPS surveys, the illustrations include Henry VIII's private chamber and the original St George's Chapel - where the Prince and his American sweetheart will tie the knot on May 19.
WINDSOR CASTLE IN ITS EARLIEST FORM, 1086: This illustration shows Windsor as a motte-and-bailey castle - 'motte' being a mound, and 'bailey' an enclosed courtyard. It was a defensive fortress built by William I (reign, 1066-1087) circa 1086 to guard the Thames valley against any marauding Saxons bold enough to challenge his supremacy. He chose the commanding spot on top of a 100ft cliff overlooking the River Thames which provided easy access to the capital. William first built up a mound of earth to create an artificial hill and then erected a wooden palisade (staked structure) above it. At the base was a ditch, which could be filled with water if necessary, as a defensive measure. Surrounding the base, within the lower walls, was the bailey. Beyond the walls lay several homesteads, which may have acted as a gatehouse, along with several fields for the rearing of livestock. The site had a large staff of servants and defenders and also served as a marketplace for the townspeople, which created growth in the area. The main route from the fort led down to the river for the transportation of goods for trading in London. All that remains of this structure today is the mound on which Windsor Castle's iconic Round Tower stands
THE CASTLE DURING THE SIEGE OF 1216. The failure by King John (reign, 1199–1216) to honour the commitments set out in the Magna Carta led to civil war. The rebel barons offered the throne of England to Louis, son of Philip II of France, who landed at Sandwich with a French army in May 1216. This drawing shows Windsor Castle during the two-month siege by Louis's army. By 1100, Henry I had built domestic quarters within the fortress, while his grandson Henry II transformed it into a palace in the late 12th century - including replacing the timber walls with stone. He built two sets of royal apartments - a public residence in the Lower Ward (to the left) and a smaller private residence on the north side of the Upper Ward (right) exclusively for himself. By this stage, walls and towers had also been constructed along the three sides of the upper bailey (the courtyard area seen to the right). Also visible is one of Windsor's most famous features - the Round Tower crowning the central mount - which was built by Henry II. In addition, the late 12th century gave rise to lodging for the king, a chapel, kitchens and Great Hall
CASTLE DURING THE REIGN OF HENRY III: The reign of Henry III (1216–72) ushered in a richer era in the history of English royal building and court culture. He improved the royal apartments, renovated many of the other buildings and further fortified the stone walls. Research has shown that much of the Castle's 12th- and 13th-century masonry, illustrated in this drawing, survives within the present buildings - with St George's Chapel (seen centre in the Lower Ward section) inside the walls. The chapel was built in the 1240s by the king. From 1222 onwards, extensive work was carried out on the great hall in the outer bailey, the 'king's houses,' the 'houses on the mount,' and the tower enclosing them. New towers were also built, which were then connected by a strong, curved wall for defence. The entrance complex (bottom centre) was built between 1220 and 1245
An engraved depiction showing two views of Windsor Castle circa 1660. During the Civil War of 1642–51, the castle was occupied by Parliamentarians and used as a prison to hold Royalist supporters
Windsor Castle is the oldest and largest occupied castle in the world, set in 10.5 hectares, and has been home to 39 monarchs
HENRY VIII'S PRIVATE CHAMBER, 1540: Henry VIII (reign, 1509–47) was a frequent visitor to Windsor, enjoying hunting and hawking in the surrounding parks and forest. This artist's impression of the King's private chamber in the Henry VII Tower, built during his father's reign, shows painted and gilded wood and stonework, and richly embroidered tapestries on the walls. The room would have been part of the monarch's inner sanctum, where Henry met with close advisers such as Thomas Cromwell (who is seen, above, to the right)
GREAT CHAMBER IN THE REIGN OF EDWARD IV, 1476: In the medieval period, the King's Great Chamber (today, the location of the Queen's Audience Chamber and Queen's Presence Chamber) was central to the life of the castle, and the setting for public audiences and court entertainment. This artist's impression shows the room being prepared for the Garter feast of April 28, 1476, during the reign of Edward IV (1461–83). The room was probably quite plain, but when the court was in residence it was transformed with rich wall hangings, furniture and gold and silver plate. Here, the wall hangings are decorated with the motif of the Order of the Garter, the oldest and most senior Order of Chivalry in Britain, founded by Edward III at Windsor
PAINTED CHAMBER IN THE ROSE TOWER, 1366: Edward III (reign, 1327–77) - the 'warrior' king - is best known for his lengthy campaigns in France during the Hundred Years War. He spent £50,000 transforming Windsor into a Gothic palace, rebuilding the Castle's Upper Ward to include square towers and high octagonal stair turrets. This illustration shows the small octagonal 'Painted Chamber' of the Rose Tower (today known as King John's Tower) in Edward III's day. The colour scheme is based on a surviving fragment of decoration, which suggests that the walls were covered with a pattern of almond-shaped panels containing red, green and gold roses on a red background
Harry and Meghan (left, earlier this week at Westminster Abbey to commemorate Anzac Day) will marry on May 19 at St George's Chapel, in the grounds of Windsor Castle in Berkshire
The Queen receives President of Estonia Kersti Kaljulaid during a private audience at Windsor Castle in March
From Elizabeth I's long gallery to a travelling circus: Windsor Castle over the years
- Windsor Castle is the oldest and largest occupied castle in the world, set in 10.5 hectares, and has been home to 39 monarchs.
- Notable changes to the castle include Elizabeth I's long gallery, built in 1583 for the Queen to take walks in bad weather; Charles II's creation of grand baroque apartments, which began in 1673 and took 11 years to complete, and the new State Entrance constructed during Queen Victoria's reign in 1866.
- During the reign of Henry II (1154–89), a vineyard was planted to the south of where the Round Tower stands today. Rather than the superior 'clear wine' imported from France for the King's table, the vines yielded 'ordinary wine' that was given to the Royal Household's higher servants.
- During Edward III's major renovations of 1351, a new clock was installed at Windsor to regulate the life of the castle and court. One of the first clocks to be made in England, its bell was built in London before being shipped up the Thames to Windsor in February 1352. Edward commissioned other clocks, including one for the Palace of Westminster.
- An excavation in 2006 by Channel 4's Time Team programme, in the south-east corner of the castle's Upper Ward, revealed part of the foundations of a large circular structure. The measurements of the structure corresponded closely to the dimensions of the building that was intended to house Edward III's new Round Table, a meeting place for knights belonging to the Order of the Garter.
The Queen Mother inspects the 300th Anniversary Parade of the Grenadier Guards at Windsor Castle with Prince Charles, Princess Anne and Princess Margaret in 1956
- Windsor Castle was a favourite residence of Elizabeth I. Hans Eworth's Elizabeth I and the Three Goddesses, 1569, is thought to include the earliest painted representation of the Castle.
- During the Civil War of 1642–51, the castle was occupied by Parliamentarians and used as a prison to hold Royalist supporters. Prisoners' graffiti is still visible today in a room above the Norman Gate.
- Windsor Castle first became a tourist destination between 1714–76, when the court and royal family rarely visited. Visitors came by coach or barge from London to walk along the terraces, view St George's Chapel and tour the State Apartments led by the Housekeeper. The first guidebook was introduced in 1749.
- In 1747, the Italian artist Canaletto visited Windsor to record the castle for Sir Hugh Smithson, one of Canaletto's most important patrons in England.
- A 1763 inventory of the Round Tower apartments of the castle's Constable and Governor, the Earl of Cardigan, includes a room for his servant Ignatius Sancho, a composer, actor and writer. Sancho was the first-known Briton of African heritage to vote in a British election and lobbied for abolition of the slave trade.
- The appearance of the Round Tower dates from the major remodelling of Windsor in the 1820s by George IV. In line with the king’s romantic notion of castle architecture, the tower was heightened by nine metres and given Gothic-style battlements.
- In June 1887, George Sanger's travelling circus paraded in the Quadrangle before Queen Victoria and her grandchildren, and gave a performance on the East Lawn. In her journal, the Queen describes 100 horses, 50 ponies, seven elephants, five lions, three camels, a cage of tigers, leopards, a puma, a kangaroo, a monkey, three llamas and an Indian bull.
- In 1911, Queen Mary persuaded King George V to reintroduce weekly band concerts for the public, which had last taken place at the castle during George III's reign.
- In 1924, Queen Mary was presented with a dolls' house designed by Sir Edwin Lutyens as a gift from the nation. After its display at the British Empire Exhibition at Wembley, the miniature house was installed permanently at the castle.
- During the Second World War, the Royal Archives were evacuated from the Round Tower to an underground space beneath the castle known as the South Bowe.
- In addition to being an official royal residence and one of the principal homes of the Royal Family, Windsor Castle encompasses St George's Chapel and has been home to the College of St George since 1348. In total, more than 160 people live within the precincts of the Castle as part of a community that has been based there for seven centuries.
Fire broke out at the castle, damaging more than 100 rooms, in November 1992, in a year described by the Queen as her 'annus horribilis'