Norwich Castle.
Norwich Castle presides over the city from its mound, which was once much more prominent compared to the buildings around it. In the Middle Ages, the Castle's limestone cube and the Cathedral's limestone spire would have dominated the city, many times larger than any of the dwellings or parish churches below on the floor of the Wensum valley.

The Castle viewed from St Peter's Street in 2021, during repair works (hence the crane).
The Normans arrived in England, as everyone knows, in 1066, and set about consolidating their victory after the Battle of Hastings in October. The government they set up was not a government in the sense we know it today—it was not about running the country, or providing any sort of service for citizens. It was quite openly a matter of extracting as much wealth as possible from the people of England. This was initially through good old fashioned pillaging and plunder, in the tradition of their ancestors the Vikings who had marauded through East Anglia a few centuries before.
But once their armies were safely installed, the Normans employed some more sophisticated robbery techniques: namely, taxes and the aristocracy. By right of conquest, William now claimed the entire Kingdom of England as his own. He carved portions of the country up and generously gave them to dukes, bishops and earls, who would levy taxes for him and do the actual business of extracting wealth and crushing opposition, in return for a hefty share of the profits.
The dukes, bishops and earls in turn recruited their own deputies: barons, knights and abbots. In this way, the Normans' naked gangsterism became an efficient wealth-generating machine. Every member of society had a rigidly-defined place in the hierarchy which determined how much they gave to the people above them, and how much they took from the people below them. Obviously this was not some brand-new invention; feudalism had existed long before the Norman conquest of England. But these techniques were more intricate, lucrative and secure than the ones used by the Anglo-Saxon thegns and warlords. They guaranteed centuries of returns on William's investment.
This history may seem irrelevant, but keep in mind that the Norman profit-lust was a tangible force that shaped our landscape and society. It manifests today, not only in pretty medieval architecture, but also in the legal system, in the foundations of our politics, in the division of land and property, in the layout of cities, in the hedgerows that divide the farms beyond the outer ring-road. Try as we might to alter the city and its society, we are working within the frameworks that they made for us.
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William the Conqueror's regime was by no means stable—almost immediately after the Conquest, he faced challenges from his bishops and dukes. There was everything to gain here. There were Anglo-Saxon rebels too, notably Hereward the Wake, a native of Ely and a favourite of romantic nineteenth-century historians, but they were easy to subjugate. One of the first things William did once his troops arrived in East Anglia was to order the construction of a motte-and-bailey palace at Norwich to show the rowdy natives their place. Just for good measure, the new castle was constructed on the ruins of an Anglo-Saxon settlement. As many as 100 houses were destroyed to make way for the foundations, which used existing Roman and Saxon earthworks.
Ralph de Guader was put in charge of the new castle. He was a Breton nobleman, born in England before the Norman Conquest. As a non-Anglo-Saxon, with interests on the other side of the Channel, he was created Earl of the East Angles after the Conquest. He was also known variously as Earl of Norfolk and Earl of Norwich.
William I returned to his homeland of Normandy during the 1070s, but while he was away Ralph de Guader married Emma, the daughter of the Earl of Hereford, without William's permission. These were two powerful families; the Earl of Hereford, William FitzOsbern, was the King's cousin and one of his most powerful magnates, who had fought beside him at Hastings. The union of the FitzOsberns and the de Guaders was too much for the King to countenance, and he sent messengers to Norwich indicating that he refused the match. Ralph and Emma were wedded anyway, and immediately began amassing troops to overthrow William I.
Ralph's army was quickly crushed at Cambridge by the warrior-bishop, Odo of Bayeux—the man who probably commissioned the Bayeux Tapestry, and who would soon fall out with the King himself. Odo and the Norman lord Geoffrey de Montbray ordered that all Ralph's captured rebels be punished by having their right foot cut off. Ralph himself fled the country via Norwich, heading for his native Brittany, where the Normans held no power.

Bishop Odo of Bayeux, photographed in action at the Battle of Hastings. He has a club, not a sword, because holy men were not allowed to draw blood, although this didn't stop an entire class of warrior-bishops from prancing around killing people during the Conquest.
Meanwhile, Emma de Guader was left defending Norwich Castle. Odo and Geoffrey's armies descended on Norwich, and the Castle saw its first military action, a few years after it was built. Emma, to her credit, held the Castle admirably during a three-month siege, while the rest of Ralph's co-conspirators left the country or surrendered and were executed. Eventually, Emma negotiated a surrender to the Norman forces, on the condition that she and her entourage were allowed safe passage out of the castle and then out of the country. Her demands were granted, and she left Norwich forever in a blaze of glory.

A 'guerilla plaque', put up in 2019 by the Common Lot feminist theatre company to commemorate Emma de Guader, among other Norwich women.
The next several centuries in the history of Norwich Castle were less heroic. The only other military action seen by the Castle during the Middle Ages was in 1174, when Hugh Bigod, the newest Earl of Norfolk, joined a rebellion against King Henry II. He raised an army of 500 Flemish mercenaries and captured the Castle, holding fourteen prisoners for ransom, but his rebellion was ultimately unsuccessful.
The Castle was rebuilt around this time as a cube-shaped keep, faced with cream-coloured Caen limestone like the Cathedral. It became a royal prison during the 13th century and remained so for over six hundred years, seeing the execution of Robert Kett and the notorious Norfolk murderer James Rush, among others. In the 1770s the prison reformer John Howard visited the Castle six times, recording an average of 40-50 prisoners. He observed:
There is a dungeon down a ladder of 8 steps, for men-felons; in which has sometimes been an inch or two of water ... Only a small room for women-felons; and they cannot be seperate from the men, when decency would most of all require it ... The gaoler is humane, and respected by his prisoners. These, felons as well as debtors, sell from the grates of their separate day-rooms, laces, garters, purses, nets, &c. of their own making.

An illustration of Norwich Castle from atop the mound, by Francis Grose. October 1775.
The Castle decayed during its time as a prison. Numerous extensions and satellite buildings were constructed around it, and circling the foot of the mound, but the central keep rotted. The Caen limestone had long since been stripped away to reveal the flintwork beneath. In 1834 the outside of the Castle was restored with Bath stone, creating the pale exterior we all know today, that seems to glow over the rooftops at sunset. Six-and-a-half centuries of continual use as a prison came to an end in 1887, when HMP Norwich opened at the Britannia Barracks on Mousehold Heath.
After this, the prison block at one end of the Castle was partly demolished and the remainder converted into a museum and art gallery. Inside is a huge taxidermy collection; a group of scene paintings of the Norfolk Broads by Nugent Monck; a collection of vivid and disturbing needlework pieces by Lorina Bulwer, an inmate in a Great Yarmouth lunatic asylum during the 19th century; and the Happisburgh Axe, which is the oldest man-made object in Britain. It was hand-carved from flint, five thousand centuries ago, by an anonymous resident of Doggerland, the ancient woodland that joined the wilds of Britain with mainland Europe. It looks almost like a precious stone.
Now, in the age of smartphones, electric cars and climate chaos, the Castle has been closed for repairs for the last 18 months, with a crane hanging over the mound.