The nearly 1000-year-old Tower of London inspires many reactions, among them awe, horror, and intrigue. William the Conqueror built the White Tower in 1066 on the River Thames as a symbol of Norman power and dominance. Over the centuries, the structure expanded into 21 towers. The UNESCO World Heritage Site is a landmark in London that millions come to see every year.

The impenetrable fortress has played many roles over the years, serving as a royal palace, a menagerie, a prison, the Royal Mint, and a repository for royal documents and jewels (the royal jewels, including the Imperial Crown, housed here cost $32 billion). Here are seven facts you may not know about the Tower of London.

1. The Tower of London has held notable prisoners.

From royals accused of treason and religious conspirators to common thieves and even sorcerers, many people have been incarcerated in the Tower of London, but the experiences differed—some were tortured and starved, while others were waited on by servants. And, of course, there were executions. Three queens were beheaded at the tower in the 16th century. Elizabeth I was just 2 when her mother Anne Boleyn was condemned to death by her husband, King Henry VIII. The king later also beheaded his fifth wife, Catherine Howard. The third rolling regal head was of proclaimed queen Lady Jane Grey, also known as the “Nine Days’ Queen,” who was 17 when she was charged with high treason by Queen Mary I.

Queen Mary also imprisoned her half-sister Elizabeth I in in the tower in 1554, but she escaped her mother’s violent end due to lack of evidence. In 1559, when Queen Mary passed away, Elizabeth came back to the Tower, this time for preparations for her coronation.

The last execution took place more recently than you might think: It occurred in 1941, when German spy Josef Jakobs faced a firing squad. In 1952, gangster brothers Ronnie and Reggie Kray were among the last prisoners to be detained in the tower.

2. A Catholic priest escaped the Tower of London in 1557 using invisible ink.

During the reign of Protestant Queen Elizabeth I, the persecution of Catholics led to the incarceration and torture of Jesuit priest John Gerard. His escape is still a wonder—he sent notes to his fellow prisoner John Arden and outside supporters with an invisible ink made of orange juice, which revealed his secret messages when held to a heat source. He later used a rope to get to the boat waiting across the moat. HBO’s series Gunpowder depicts this prison break in the second episode.

3. The Tower of London once had a zoo that was home to a now-extinct subspecies of Barbary lion.

You won't find any live lions at the Tower of London today.petekarici/Getty Images

In the 1200s, King John started the royal menagerie in the Tower of London to hold the exotic animals gifted by other monarchs. It became an attraction for Londoners who came to see captive lions and the white bear, who was regularly taken to the Thames to hunt. The menagerie closed in the 1830s and the royal gifts were re-homed in the London Zoo. As a nod to this legacy, the Tower exhibits animal sculptures by artist Kendra Haste.

In 1936, excavations around the moat led to a fascinating discovery: two lion skulls dating to the medieval times. Genetic evidence suggests they belong to a subspecies of Barbary lion that once lived in Africa but disappeared a century ago.

4. In 2014, the Tower of London organized the Centenary Commemoration of World War I with 888,246 poppies.

Five million people came to see the art display of ceramic poppies in the moat, all created by artist Paul Cummins. Each poppy denoted a British military fatality in the war. They were sold for £23 million (each individual poppy was £25) to raise money for armed forces charities. However, a controversy arose when it was revealed that a whooping £15 million was spent on costs (Cummins made £7.2 million) and the charities only received £9 million.

5. In 2019, 500-year-old skeletons were unearthed under the Tower of London’s chapel.

Archeologists found two skeletons, an adult woman and a child, near the same spot where the headless body of Queen Anne was also laid to rest. The bones were thought to be buried somewhere between 1450 and 1550 and give an insight into the lives of the common folk who lived at the tower in the medieval times.

6. Beefeaters live in the Tower of London with their families.

A 19th-century illustration of the vibrantly clad Yeomen Warders at the Tower of London.duncan1890/Getty Images

The Yeoman Warders (also known as Beefeaters) have been guarding the Tower since the Tudor era. Clad in a sharp red dress, these 37 men and women give tours of the fortress. Every night at 9:53 p.m., they lock the tower, a 700-year-old tradition called the Ceremony of Keys. Beefeaters and their families, around 150 people in total, live in the supposedly haunted Tower of London, and also frequent a secret pub in the fortress.

7. There’s a superstition that if the ravens leave the Tower of London, the kingdom will fall.

According to legend, in the mid-17th century, King Charles II was warned that the Crown would fall if the ravens ever left the Tower of London—so he ordered that six of the birds be kept captive there at all times, as he believed they were a symbol of good fortune. (However, some sources claim this tale is Victorian folklore, while others maintain the legend was created even later, during World War II.) Today, there are seven ravens (one spare) living in the Tower of London, in an aviary on the grounds. The ravens’ primary and secondary wings are trimmed carefully, so they can fly but stay close to home, where they feast on blood-soaked biscuits and meat.

In the past, ravens have gotten away—one took flight to Greenwich but was returned after seven days, and one was last seen outside an East End pub. Now with fewer visitors after the coronavirus-induced lockdowns, ravens are getting bored and two adventurous birds have been straying from the Tower, much to the distress of the ravenmaster.