Image copyright Herbert Walker Image caption Captain Herbert Walker, seated on the right, in Benin City after British troops looted the palace

At the end of the 19th Century British troops looted thousands of works of art from the Benin Empire - in modern-day Nigeria - and brought them home. One soldier's grandson inherited two bronzes but recently returned them to their original home.

"It's an image that's deeply ingrained in my memory. The dead body seemed unreal. It's not a picture you can easily forget," says Mark Walker.

He was 12 years old when he first saw his grandfather's diary - the photographs inside made a deep impression.

"They were very faded, but perhaps the most shocking one for me was a partly dried-up body being held up by two men on a pole.

"Clearly the people lifting the body didn't actually want to touch it and that seemed to me to capture the feeling my grandfather also had about them. It was something so horrible you wanted to keep it at arm's length," says Mark.

The pictures were taken by his grandfather, Capt Herbert Walker, in West Africa in 1897.

The two Walkers never met - Herbert died in 1932, 15 years before his grandson was born and Mark's grandmother showed him the journal, titled To Benin and back, while he was staying with her in 1959.

Image copyright HSW

The Benin Kingdom, which is now part of Nigeria, had a wealth of natural resources including ivory, palm oil and rubber which the UK was keen to control.

Find out more Mark Walker spoke to Witness on BBC World Service Radio

But in January 1897, seven British officials who were on their way to see the Oba of Benin - the king - were killed in an ambush.

The Times of London reported that the men "on quite a peaceful mission" had been "massacred by the King's people".

It is unclear who, if anyone, ordered the killings and there are indications that the mission was not as peaceful as the British press described it. Although its leader, acting Consul-General James Phillips had sent a message to the Oba asking to discuss trade and peace, he had told London he wanted to depose him.

The killing of Phillips and his men provoked a devastating response - the UK decided to punish the Oba, Ovonramwen, and launched the Benin Punitive Expedition.

It sent almost 500 men to destroy Benin City - Herbert Walker was one of them.

After 10 days of fighting Ovonramwen fled.

Image copyright HSW Image caption Capt Walker kept a diary during the Benin Punitive Expedition

"The city is the most gruesome sight I've ever seen," wrote Herbert. "The whole pace is littered with sculls & corpses in various stages of decay, many of them fresh human sacrifices. Outside the king's palace were two crucifixion trees, one for men & the other for women, with the victims on & around them. As we approached the city through the bush, we found bodies of slaves newly sacrificed & placed across the path to bring the Benis luck, while they lay in holes, or behind cover, & 'sniped' at us as we passed."

It was a photograph of this scene that Mark saw six decades later. According to Herbert, the sacrifices were carried out by the people of Benin to appease the Gods while they tried to ward off the attack by the British army.

It's not clear how many Benis died in the fighting - no official count of the bodies was carried out. But some Nigerians have called it "the most brutal massacre of the colonial era".

"The British had much better weapons so it was something of an uneven battle," says Mark, a retired doctor from Wales.

Herbert's diary describes how the British fired Maxim machine guns and rockets at their enemies.

Image copyright Tom S. Gardner Collection Image caption The British exiled the Oba of Benin to Calabar after his trial

After the killing came the looting - the British seized more than 2,000 artworks and religious artefacts, most of them hundreds of years old, which were sent back to England.

Herbert describes how a fellow officer "is now wandering round with chisel & hammer, knocking off brass figures & collecting all sorts of rubbish as loot". Religious buildings and palaces were torched.

The Oba was eventually exiled to Calabar in south-eastern Nigeria, after a British court acquitted him of the killings that sparked the attack. But by the time the monarchy was restored in 1914, the independent kingdom of Benin no longer existed - it had become part of Nigeria, which was then a British colony.

Image copyright British Museum Image caption Eight-hundred items eventually ended up in the British Museum in London

Most of the objects taken from his palace were sold in Europe and about 800 of them eventually ended up in the British Museum where they are still on display.

The museum's director, Neil MacGregor, has said it was a "revelation" to Western scholars that refined metal work such as this had been made in 16th Century Africa.

A few of the artefacts were kept as souvenirs by the officers who were there - Herbert held on to two pieces, a so-called "bird of prophecy", known as an Oro bird, and a bell used to invoke ancestors.

Mark inherited them in 2013. "I was surprised, having coveted them for so many years that when I finally came in possession of them I found myself asking what their future was," he says.

His children weren't interested in them and he did not want them sold at auction after his death.

Image copyright Mark Walker Image caption Mark Walker returned a so-called "bird of prophecy" to Benin City

"As you come into your 60s you realise you have got to start making preparations for moving away from this life. I was asking myself, 'What do I want them for?' Possessions aren't as important as I used to think when I was younger," says Walker.

He came across the Richard Lander Society, an organisation that campaigns for the Benin artworks to be returned to the royal palace in Benin City. It helped him contact the right people and last year Walker travelled to Nigeria to hand the bronzes to the present Oba, the great-grandson of the King deposed by Herbert and his colleagues.

"It was very humbling to be greeted with such enthusiasm and gratitude, for nothing really. I was just returning some art objects to a place where I feel they will be properly looked after," says Mark.

Image copyright Mark Walker

But in the minds of the people of Benin City it wasn't nothing.

"Those things that were removed were chapters of our history book," says Prince Edun Akenzua, a younger brother of the current Oba.

"When they were made, the Benin people did not know how to write, so whatever happened, the Oba instructed the bronze casters to record it.

"We saw the removal as a grave injustice and we are hoping that someday people will see why we are asking for these things back," he says.

Prince Edun has lobbied the British Parliament for all the looted items to be returned to Benin City and argues that the British Museum should keep replicas instead.

"The English returned the Stone of Scone to Scotland some years ago. So why can't they return our things? They mean so much to us but they mean nothing to the British," he says.

Image copyright British museum

The art of the kingdom of Benin

The British Museum holds 800 pieces including bronze, ivory, clay, wooden, and iron objects

Its collection was developed over many years - some items were donated in 1898 and many more in the early to mid-20th Century

The kingdom of Benin dominated trade between the Nigerian coast and Europe from the late 1400s to the end of the 1900s

Portuguese traders arrived in Benin in the 1400s bringing brass bracelets, known as manillas , to exchange for pepper, ivory and slaves

, to exchange for pepper, ivory and slaves The artists of Benin melted them down to create objects to decorate the Oba's palace

The British Museum says it has not recently received any new official requests for the return of the Benin Bronzes to Nigeria.

"As a museum of the world for the world the British Museum presents the Benin Bronzes in a global context alongside the stories of other cultures and makes these objects as available as possible to a global audience," it says in a statement.

One argument that has been put forward is that the objects are in danger of getting lost if returned to Nigeria, something Prince Edun dismisses as absurd.

"It's a bit like if someone were to steal my car in Benin City and I found it in Lagos, and could prove that it was mine. And the thief told me, 'OK, you can have your car back if you can convince me that you've built an electronically controlled garage to keep the car. Until you do that, I will not return it to you.'"

Image copyright AFP Image caption Prince Edun Akenzua (left) met with Mark Walker in Benin City to receive the bronzes

There are plans to establish a museum in the Oba's palace where returned items can be put on public display.

Looking back, Mark says he feels no shame at his grandfather's part in the Benin Punitive Expedition.

"His diary shows that he had a sense of humanity rather than what I was expecting to find - a shared sense of racial superiority.

"We are taught from a very young age that the killing of enemy combatants under the umbrella of statehood is a regrettable necessity of life," he says.

Image copyright HSW Image caption One of the photographs in Herbert Walker's diary

As for the looted artworks, he believes his grandfather did what everybody else did at that time.

"To him, it was probably no more than picking up stuff that's washed up on the beach, because people had fled and nobody owned them any longer."

But he is happy they are now back in Benin City. "These objects are part of the cultural heritage of another people… to the people of Benin City, these objects are priceless."

Mark Walker spoke to Witness on the BBC World Service.

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