TODAY, we tend to view the manacles and chains that were used to control African slaves on the long, terrible sea voyages from Africa across the Atlantic as symbols of their subjugation and submission.

But they can also be viewed in an entirely different light, says James Walvin, a retired professor of history from the University of York: as symbols of defiance.

The slaves crammed into hellish conditions in the holds of slave ships hadn’t all been brutalised into submission. Many, especially the young men, were extremely angry at what had happened to them – and posed a constant danger to the ships’ crews.

Europe’s iron industries produced vast quantities of chains, fetters, manacles and restraints. “It was these… which enabled sailors to ship huge numbers of Africans to the Americas,” Prof Walvin writes in his new book, The Slave Trade. “Without the manacles and chains, the crews would surely have been overwhelmed, so it is worth thinking of chains also as a symbol of African defiance.”

These were men, and women, and children, who had been born free, in other words. They did not go easily into the hell that was slavery.

As Prof Walvin’s book makes clear, the conditions on many slave ships were appalling.

Chained below decks in unimaginably cramped conditions, occasionally taken up on deck and exercised in small groups, ignored completely during bad weather when the crew were all hands on deck, many would not survive the long voyage.

“Disease spread easily in the filth of communal incarceration,” Prof Walvin writes. “The Africans – numbered, rarely named, in the ships logs – succumbed to a variety of diseases, but especially dysentery (‘the bloody flux’). Corpses were simply thrown overboard as the ship struggled westwards. Not surprisingly the slave ships stank: their notorious stench could be detected miles downwind.”

Little wonder that the ship’s crews – there could be as few as ten men to control 200 slaves – were terrified of their charges. Control and discipline were brutal, but even so, revolts occurred on something like one in ten slave ships, Prof Walvin says – mostly when the ships were still in sight of the African shore.

Reprisals were savage: public shootings, dismemberment and beheading, as much to terrify the surviving slaves as to punish the rebels.

The slaves who survived and made it to the Americas had little to look forward to but a lifetime of bondage on the sugar or tobacco plantations of the Caribbean or the cotton fields of the southern USA.

A sheaf of facsimile documents at the back of Prof Walvin’s book – which is part of Thames & Hudson’s popular History Files series – is enough to send a shiver down the spine. They include a poster advertising an auction of slaves at the courthouse in Charleston, South Carolina, at 12 o’clock on January 11, 1859. There are 99 slaves listed, ranging in age from one month to 70 years – a slave known as ‘Old Peter’ .

Profit drove the slave trade – not only from sugar, tobacco and cotton, which slave labour made possible, but also the associated industries, among them ship-building and iron-production (for all those chains and manacles).

Much of the wealth of the first British Empire was founded on the slave trade, Prof Walvin says. And some of the country’s greatest houses – including Harewood – were built on the proceeds.

In all, between 1500 and 1860, about 12 million Africans were loaded on to slave ships bound for the continent. Throughout much of that time, the trade was not seen by the vast majority of people as in any way immoral. But gradually, perceptions changed. Under the influence of enlightened thinkers such as Yorkshire’s own William Wilberforce, the trade was eventually abolished.

Prof Walvin’s slim, 130-page book is packed with drawings, sketches and cartoons which bring this odious trade to life. A young negro girl is shown hanging by her foot from the mast of a ship, punishment for some unknown act of rebellion. Overseers wield whips; buyers are drawn inspecting slaves at an auction in Charleston; slaves are pictured crammed in squalid misery into the hold of a ship.

The book makes you wonder, yet again, how such a trade could have been tolerated for so long. And yet it was.

• The Slave Trade by James Walvin is published by Thames & Hudson, priced £12.95