Tradition has it that as long as the ravens remain at the Tower of London, which they have occupied since the fortress first stood along the River Thames, the kingdom will persevere. Today, the huge black birds, sporting names like Hardey, Odin, Gwyllum and Cedric, wander the inner courtyard of the Tower, their wings clipped to ensure their continued residence. As with the ravens, the Tower of London also endures, despite assaults in the 13th and 14th centuries and more recently, aerial bombing raids during the Second World War. The fortress's battlements command international attention, for this majestic World Heritage Site embodies the history and spirit of the land it represents.

The proper title is "Her Majesty's Royal Palace and Fortress of the Tower of London" and it has dutifully served the monarchy since the 11th century. That was when William the Conqueror ordered the construction of stone keep to command his new kingdom. Planting his castle in the corner of the walls that enclosed the Roman city of Londinium, William I began one of the realm's earliest and possibly finest, stone keeps. Later known as The White Tower after the brilliance of its whitewashed walls, the Norman keep retains its classical rectangular design and forms the centrepiece of this great fortress on the Thames.

Altered over time, the 90 foot high tower initially provided accommodation for the king and the castle's constable and even housed important prisoners in its finer upper chambers, for example the Duke of Orleans, who resided there in the 15th century. Meanwhile, with its 15 foot thick walls, the basement was used occasionally to imprison less savoury characters. On the second storey, the Chapel Royal of St. John the Evangelist with its smooth unpainted walls, bestows grace and dignity upon this great keep.

Over time, succeeding monarchs surrounded the White Tower with towered walls, palatial buildings and a military depot but the turreted keep has always remained the castle's most recognizable feature. Both physically and visually, its owners intended the Tower of London to dominate, intimidate and impress onlookers. Every angle reinforced the notion that here stood a royal stronghold with no rival.

In the 13th century, Henry III began an ambitious expansion program at the site, adding a massive curtain wall that had nine sturdy towers and doubled the size of the fortress. He contributed a new Great Hall, a kitchen block and additional accommodations. He flooded the moat with the waters of the River Thames and enclosed the Church of St. Peter ad Vincula within the curtain wall. He also established a royal menagerie inside the castle which housed an elephant, bears, lions and other exotic animals that were presented to him by the crown heads of European nations.

Later in the 13th century, Edward I transformed the Tower of London into a fine concentric fortress like those he built in North Wales. Edward was a castle builder at heart and he undertook the redesign of the castle. First he filled in the moat that Henry III had flooded and enclosed the fortress with yet another - albeit lower - towered curtain that was fitted with heavily defended twin-towered gatehouses. He also added St. Thomas's Tower, which had a water gate for access to and from the River Thames. Now know as Traitor's Gate, this access gained its name from the prisoners who passed through on their way to confinement and execution. Among the most famous of these prisoners under Henry VIII's reign were Anne Boleyn, Catherine Howard and Sir Thomas More, after whom the tower was named.

Edward I also built a royal mint inside the castle and added a treasury to house the Crown Jewels. Now housed in the Jewel House, the Crown Jewels remain one of the Tower's biggest attractions. The Tudor kings expanded the Tower of London's role as a prison and staged scores of political executions on Tower Green and Tower Hill. Today a plaque commemorates the 125 prisoners who lost their lives there.

By the late 17th century, the castle's role as a state prison diminished. The Office of Ordnance began to occupy the site and with them came munitions stores, military workshops, a barracks and gun batteries. In the 1840s the Army constructed the North Bastion, Waterloo Barracks and other structures to counter local civil unrest from the Chartist Movement. Beginning in the 1850s, Queen Victoria and Prince Albert began restoring the castle's medieval appearance.

Visit the Tower of London today and you will be regaled by the Beefeaters with stories of treason, beheadings, torture and ghostly apparitions. Managed by the Historic Royal Palaces, the Tower is open daily throughout the year for an entrance fee.