By Jonny Lupsha, News Writer

New ravens have hatched in the Tower of London for the first time in 30 years, the tower’s official website said. A superstition-based royal decree dating back to Charles II mandates that at least six ravens bred by a ravenmaster must live on the grounds at all times, lest England fall to calamity. The Tower of London is steeped in history.

When Charles II proclaimed in the 17th century that at least six ravens must live on the castle grounds of the Tower of London, the structure was already over 1,000 years old. The four new birds that were bred and hatched this April join a long tradition of the grounds—but ravens are just one of many fascinating secrets the tower holds.

Building Britain’s Most Famous Castle

One of the most popular images of a traditional castle is that of the stone keep. “Several built in the 1100s survive, including those at Dover, Oxford, and the Tower of London,” said Dr. Patrick N. Allitt, the Cahoon Family Professor of American History at Emory University. “The Tower, begun in 1070, is almost a cube: 107 by 118 feet at the base, and 90 feet tall.” A 90-foot-tall keep may not seem impressive by today’s standards of epic fantasy films and television series, but it was a substantial structure for the early 12th century.

Structures built in this period that are similar to the Tower of London are also notable for their sturdy walls. “The walls of these stone towers are often 10 feet thick, meaning that they feel oddly smaller inside than they look from the outside,” Dr. Allitt said. “The benefit, of course, was that no siege engine could knock down a structure so immensely strong.” That long ago, invading armies lacked the explosive prowess necessary to blow up the walls as well. The only option was to dig tunnels under the towers’ walls and hope for a partial cave-in of the structure itself.

According to Dr. Allitt, the next step in tower design was to add outer walls to further fortify the castle grounds. “The Tower of London was made safer and stronger by having the keep enclosed by an outer wall during the reign of King Henry III,” he said. “When a second wall outside that one was added by his son Edward I, it became stronger still.” From an aerial view, it’s possible to see the evolution of the Tower of London as it spreads outwards, like counting the rings on a tree.

A History of Violence and Riches

The Tower of London also features a past whose riches outshine its bloodshed—though, perhaps, just barely.

“Here at the Tower, the two young Princes in the Tower—Edward V and his brother Richard, Duke of York—were killed by King Richard III in 1783,” Dr. Allitt said. “Here, too, King Henry VI and two of Henry VIII’s wives, Anne Boleyn and Catherine Howard, were imprisoned and killed. Also killed here were Henry VIII’s former minister Thomas More; Lady Jane Grey, only 17 years old, who briefly asserted a claim to the throne in 1553 before being ousted by Mary I; and Sir Walter Raleigh.”

On the lighter side of history, the Tower of London is home to a bevy of British valuables. “Above all other attractions rank the Crown Jewels, 141 crowns, maces, scepters, orbs, coronets, and other jeweled objects still used in royal ceremonies such as the coronation and the annual state opening of Parliament,” Dr. Allitt said. “One of them, the Sword of Mercy, was made in 1626 for the coronation of King Charles I and has been used at every coronation since then.”

Dr. Allitt strongly recommends visiting the Tower, even if you have to fight the crowds. Book ahead, see the Crown Jewels, and keep an eye out for the ravens.

Dr. Patrick N. Allitt contributed to this article. Dr. Allitt is Cahoon Family Professor of American History at Emory University. Dr. Allitt received his doctorate in history from the University of California, Berkeley. An Oxford University graduate, Dr. Allitt has also taught American religious history at Harvard Divinity School, where he was a Henry Luce Postdoctoral Fellow.