The trans-Atlantic slave trade that dates back to the 15th century has left unforgettable trauma on the African culture that still festers like a sore.

Used for years as the main slave hub, many countries expanded their colonies and transported slaves to the New World from ports in the eastern and southern parts of the continent, enduring long journeys in inhumane conditions.

Estimates of the number of African slaves carried across the Atlantic Ocean place the figure at 25 million-30 million, though the exact number is unknown.

Portugal's role

Even before Europeans started colonizing Africa, slaves had been traded on the continent for centuries, often captured in wars or among the indigenous population and sold to serve wealthy families.

Europeans added an intercontinental dimension after they set foot on the continent in the 15th century, with slave ships transporting African captives across the Atlantic in massive numbers.

The Portuguese, specifically, launched this new slave trade, selling those they captured on the coast of West Africa as slaves and organizing regular sea voyages to carry them to foreign markets, often in Brazil, the Caribbean Islands or North America.

After the discovery of the Americas and the entry of countries such as the Netherlands, Spain, Britain and France into the colonial race, the slave trade eventually became a major source of commerce.

While previously slaves who were sold from ports in East and North Africa held certain rights, the violent treatment they suffered while crossing the ocean and at the places where they arrived eventually triggered a backlash that led to the prohibition of slavery toward the end of the 19th century.

The main ports that were used in the African slave trade were located in present-day Benin, Ghana, Senegal, Gambia, Congo, Nigeria and Angola. While the Spanish and Portuguese served the main role in transporting slaves from West Africa early on, they were joined by the Dutch and British in the following centuries.

25 slaves for one horse

By the beginning of the 17th century, the number of slaves sold in slave markets in Italy, Spain and Portugal is estimated to be around 50,000, with 25-30 fetching the price of a single horse.

French traders, who began transporting slaves from Central and West Africa in the 17th century, later also gained commercial bases in Madagascar, off the East African coast.

The vast majority of the estimated 2 million slaves taken on French ships in the 17th and 18th centuries were from that island and were destined for Mauritius and Reunion Island, which today remains a territory of France in the Indian Ocean.

Island of Goree

The Island of Goree, off the Senegalese capital of Dakar, was one of the most important centers of the slave trade in West Africa.

Opened to settlement by the Portuguese in 1450, Goree was captured in 1677 by France, which held the island until Senegalese independence in 1960.

It was the "slave houses" built in 1780 that brought the UNESCO-protected island to its sad infamy today. West Africans were gathered and kept chained to each other for weeks in these houses, categorized according to their health, age and height before being shipped to the New World.

Some slaves were sent to Europe and South America on boarding ships called Tumberios, meaning "floating grave" in Portuguese.

Others were sold from slave markets for 1 kilogram (2.2 pounds) of rice or potatoes or employed in construction or household work.

Millions of Africans are estimated to have been bought and sold as slaves on Goree, the meeting point of slave traders.

Three-cornered trade

It is known that ships departing from the ports of Nantes, Rochelle, Bordeaux, Liverpool, Bristol, Amsterdam and Lisbon in Europe came to Goree Island, where young and healthy slave candidates were collected from various parts of Africa were shown off to potential buyers.

The "value" of male slaves was judged by their height, weight and muscle condition, while the criteria for women and children were their dental and general health.

The three corners of Africa, Europe and America constituted the three corners of the trans-Atlantic slave trade, with the sale of raw materials and slaves carried on for hundreds of years by France, Portugal, the British and the Dutch.

Products brought from Europe were left in Africa in exchange for the slaves in West Africa, who were then transported to agricultural lands in America in exchange for raw materials to Europe.

Many of the slaves that Britain transported to the Caribbean Islands and its new colonies in America also came from West Africa, exchanging for them high-demand items such as cloth, copper and gunpowder.

American tragedy

The clergy maintained a crucial role in slavery, especially in the U.S. For most people, it was a right granted by God to legitimate and perpetuate the system by justifying it. Even further, most of the slaves were forced to be ripped off from their identities and forced to convert to Catholicism with new Christian names.

A poem written by Phillis Wheatley, a former slave, and the first Afro-American woman to publish poetry reveals how she was so immersed in her new identity, saying: "It was mercy brought me from my Pagan land, taught my benighted soul to understand, that there's a God, that there's a Saviour too," in her "On Being Brought to America from Africa."

The Netherlands, first colonial empire in South Africa

Dutch colonizers arrived in Africa earlier than many other European countries. They were the first colonial empire in South Africa, where they numbered just 90 in 1652 before their population boomed to 16,000 by 1795.

In the same year, the number of South Africans enslaved by the Dutch in South Africa had increased to 16,839. The Netherlands, which used South Africa as a center for its slavers, took the slaves they collected to the Americas and Europe by ships, many of which docked at Cape Town.

According to historians, two-thirds of the population of Cape Town consisted of slaves in 1795.

Tanzania, the German colonial capital

The Tanzanian town of Bagamoyo was used as the capital of the so-called "German East Africa" colonial administration, which included most of present-day Tanzania, Rwanda and Burundi.

Previously largely under the control of Omani sultans from the 17th century to the end of the 1800s, Bagamoyo became one of the main slave trade hubs, boasting strategic value due to its proximity to the island of Zanzibar.

It was a center for trading in foodstuffs before the 17th century, after which it was used to meet the growing demand for slaves and elephant tusks in Europe and the Americas.

Slaves brought to the coast from the interior of Africa sometimes had to travel for months or years at a time. Exhausted and ill slaves were killed when it became clear that they could not continue on the road ahead.

They were fed a kind of nut called "bitter cola" to keep them on their feet and conserve energy along the way.

In East Africa, 23% of African slaves taken from their homes in the 19th century were taken to Arabia, Iran and India, 18% to South Africa and America, and 6% to Reunion Island and Mauritius to work in the French sugar cane fields.

Port of Bimbia, forgotten slaver hub

The Bimbia slave port, located near the city of Limbe in present-day Cameroon, is one of the forgotten historical centers of the slave trade, where 10% of the continental slave trade was conducted.

The enslaved African ancestors of well-known figures such as former U.S. Secretary of State Condoleezza Rice and famous music producer Quincy Jones also passed through the Bimbia, which is considered a part of Cameroon's national heritage.

Today, visitors can see the remains of the chains and dungeons where millions of slaves were brought from different parts of Africa to the Americas to be sold.