Zanzibar History: 2,000 Years of the Indian Ocean's Most Contested Island

Walk from the Anglican Cathedral — built on the site of East Africa’s largest slave market — to the Omani Sultan’s waterfront palace, and then a few alleys further to Mercury House, where Farrokh Bulsara was born in 1946. You are covering perhaps 400 metres. You have just crossed five centuries of Indian Ocean history, three colonial powers, a revolution, and the full arc of the slave trade from peak to abolition.

That compression is what makes Zanzibar’s history worth understanding before you arrive. Most places you need a textbook. In Stone Town you need a good guide and about two hours.

Ancient settlement and Indian Ocean trade

Zanzibar has been inhabited for at least 2,000 years. The archaeological site at Unguja Ukuu on the south-east coast of the main island (Unguja) shows occupation dating to approximately the 5th–6th century CE and is one of the earliest known settlement sites on the East African coast.

The island’s position in the Indian Ocean made it a natural waypoint in a seasonal trading system that had operated for centuries before the Portuguese or the Arabs arrived in force. The northeast monsoon — called the kaskazi locally — carries sailing vessels from the Arabian Peninsula and India down to the East African coast between roughly November and March. The southeast monsoon, the kusi, blows them home between April and October. Zanzibar sits almost exactly at the pivot point of these winds.

The result was a sustained trading relationship between the East African coast, the Persian Gulf, India, and later China. Ivory, iron, and enslaved people moved out. Chinese porcelain, Persian textiles, Indian cloth, and glass beads moved in. The evidence is visible in excavated sites across the Zanzibar archipelago: Chinese ceramics from the Song dynasty, Persian-style architectural elements, and a cosmopolitan material culture that had no equivalent in inland Africa.

Out of this coastal trade network grew the Swahili language — Bantu grammar absorbing vocabulary from Arabic, Persian, and later Portuguese and English — and the Swahili city-state culture that stretched from present-day Somalia to Mozambique. Zanzibar was a participant in this network from early in the first millennium.

There is also the Shirazi tradition: the claim by a significant portion of the Zanzibar coastal population of descent from Persian settlers from Shiraz. In 1948, approximately 56% of Zanzibar’s population reported Shirazi ancestry. Historians debate whether this represents an actual migration from Persia, a trade-mediated cultural influence, or a retrospective identity claim constructed to distinguish the long-established coastal population from more recent Arab and African arrivals. The Kizimkazi Dimbani Mosque on the south of Unguja carries a Kufic inscription dated to 500 AH (1107 CE) — one of the oldest dated Islamic inscriptions on the East African coast — which confirms a substantial Muslim mercantile presence on the island by the early twelfth century.

Portuguese arrival and control (1498–1698)

Vasco da Gama rounded the Cape of Good Hope in 1497–98, crossed the Indian Ocean with the help of an Arab pilot, and reached the East African coast in 1498. The Portuguese arrival disrupted a trade system that had functioned without European involvement for centuries.

Portugal established control over much of the Swahili coast in the early 16th century, using violence and naval firepower to displace Arab and Indian traders from the most profitable routes. Fort Jesus in Mombasa (built 1593) became the main Portuguese military stronghold on the East African coast. Zanzibar was less strategically important to the Portuguese than the Kenyan ports, but it fell within the Portuguese sphere of influence.

The Portuguese period on Zanzibar — nearly two centuries — left relatively little architectural trace compared to what followed. The major lasting impact was the disruption of the Indian Ocean trading system and the establishment of European presence in East African waters.

In 1698, Omani Arab forces under the Ya’aruba dynasty besieged Fort Jesus in Mombasa. After a long siege, the Portuguese were expelled. Zanzibar came under Omani control, and the Omanis built the Old Fort (Ngome Kongwe) in Stone Town on the ruins of a Portuguese chapel between 1698 and 1701 — the structure still stands today and is one of the oldest buildings in Zanzibar City.

The Omani Sultanate: Stone Town’s golden age (1698–1890)

Zanzibar passed from Ya’aruba to Busaidi control when that dynasty took power in Oman. Under the Busaidi sultans, Zanzibar became a major trading entrepôt. The transformation accelerated dramatically when Sultan Sayyid Said bin Sultan — who had been ruling the Omani empire from Muscat — moved his court to Stone Town. Different sources date this move variously to 1832 or 1840; what matters is that by the mid-19th century, Stone Town was his primary residence and Zanzibar his most important political and commercial base.

The consequences were significant. Stone Town was rebuilt. The elaborate carved doors that are still the city’s most visible architectural feature — teak or jackfruit wood, decorated with rosettes, geometric patterns, and (in the Indian merchant tradition) large brass studs that originated as defence against war elephants — became the mark of a successful merchant household. The Omani palace at Mizingani Road and the spice farms inland were both products of this era. The Mtoni Palace was built for Sultan Said in 1828; the Kidichi Persian Baths followed in 1850, built for his Persian wife.

Stone Town’s buildings are a physical record of those centuries of layered control. The Zanzibar architecture guide explains how to read what you see — the three carved door traditions (Omani geometric with brass boss, Indian Gujarati floral with brass anti-elephant spikes, Swahili vernacular synthesis), why the buildings are built from coral rag, and what the House of Wonders (1883, first multi-storey building in Zanzibar) and the Old Fort (1698–1701) tell you about who had power and when.

Sultan Said introduced clove cultivation to Zanzibar in the early 19th century — sources cite either 1812 or 1818, and the introduction is contested in its details. What is not contested is the outcome: by 1834, Zanzibar and the neighbouring island of Pemba produced approximately 90% of the world’s clove supply. The spice industry restructured the economy, the landscape, and the labour system of the archipelago. The economic engine behind this wealth was the spice trade — specifically cloves — and the Zanzibar spice history guide covers how cloves came from the Maluku Islands to Réunion to Zanzibar, how Sultan Seyyid Said built the plantation economy, and how the slave trade and the clove trade were structurally connected.

The spice economy required labour, and that labour was predominantly enslaved. This is the uglier side of Stone Town’s golden age: the wealth visible in the carved doors and coral-stone palaces was built on one of the largest slave-trading operations in the world at the time.

The slave trade and abolition (1800–1897)

Stone Town was the main slave-trading port of East Africa. At peak — roughly the mid-19th century — an estimated 40,000 to 50,000 enslaved people per year passed through the island. An estimated 600,000 people were sold at the Stone Town slave market between 1830 and 1873 alone.

The slave market was located in the area of Stone Town that is now occupied by the Anglican Cathedral (Christ Church Cathedral). People were held in underground chambers, inspected and auctioned publicly, then shipped onward to Arabia, Persia, India, and the clove plantations of Zanzibar and Pemba.

British pressure on Zanzibar’s rulers to suppress the slave trade began in the early 19th century. The Moresby Treaty (1822) and the Hamerton Treaty (1845) placed successive restrictions on where and to whom Zanzibar could export enslaved people. In 1872, Sir Bartle Frere was sent to Zanzibar as a special envoy to negotiate total abolition with the reigning Sultan Barghash bin Said.

On June 5, 1873, Sultan Barghash signed a treaty formally prohibiting the seaborne slave trade and ordering the closure of the slave market. The market was closed the same year. The Universities’ Mission to Central Africa purchased the site. The Anglican Cathedral — its altar positioned directly over the whipping post where enslaved people were beaten to demonstrate their endurance — was consecrated in 1879.

One historical note worth knowing before you visit: historian Jonathon Glassman has argued that the basement chambers now presented to visitors as “slave holding cells” were more likely cold storage rooms built roughly twenty years after the market closed. Other historians dispute this. The debate does not diminish the site’s memorial function — it sharpens the questions worth asking.

The 1873 treaty ended the export slave trade, but slavery within Zanzibar itself continued until 1897, when it was formally abolished under the British protectorate.

British protectorate and the world’s shortest war (1890–1963)

Britain formalised control over Zanzibar in 1890 through the Heligoland–Zanzibar Treaty with Germany — a deal in which Germany accepted British dominance over Zanzibar in exchange for British recognition of German interests in what is now Tanzania. Zanzibar became a British Protectorate, with the Sultan remaining in place as a nominally sovereign ruler under British guidance.

The most dramatic event of the protectorate era lasted less than 45 minutes.

On August 27, 1896, Sultan Hamad — who had been aligned with British interests — died. His cousin Khalid bin Barghash seized the palace immediately, raising his flag and arming approximately 2,800 men inside the palace compound. The British regarded this as an illegal seizure of power and demanded that Khalid stand down by 9:00am the following morning.

Khalid refused.

At 9:02am, British warships in the harbour opened fire on the palace. The palace was rapidly destroyed. Khalid’s wooden warship (the Glasgow, a gift from a previous sultan) was sunk. By approximately 9:40am, Khalid’s flag had been shot down and his forces had surrendered. Khalid fled to the German consulate, eventually surrendered years later in Dar es Salaam, and was exiled.

The Anglo-Zanzibar War — 38 to 40 minutes in duration — is officially recorded as the shortest war in history. Casualties were almost entirely on one side: approximately 500 Zanzibari soldiers and palace defenders killed or wounded; one British sailor wounded.

A new sultan was installed the same afternoon. The sultan’s old palace on Mizingani Road, partially destroyed in the bombardment, was rebuilt in the late 1890s in what is now the Palace Museum building.

Under the protectorate, British administration continued through a series of sultans. Slavery was abolished in 1897. Secular schools were established alongside the existing Islamic education system. The clove economy continued to be dominated by Arab landowners with African and freed-slave labour — a structure of inequality that would fuel the revolution of 1964.

Independence and revolution (1963–1964)

December 10, 1963: Zanzibar achieved independence from Britain. The Sultanate continued as a constitutional monarchy within the Commonwealth.

January 12, 1964 — one month later: A revolution overthrew the Sultan and the Arab-dominated government. The revolution was led by the Afro-Shirazi Party (ASP) under Abeid Amani Karume, with the initial military operation directed by John Okello, a Ugandan-born organiser who had been active in labour politics on the island.

The Sultan fled. Karume was elected the first President of the People’s Republic of Zanzibar, with a Revolutionary Council formed on January 14, 1964. The Arab and Indian populations — who had held most of the economic and political power — suffered violence and property confiscation in the weeks that followed. The exact casualties are disputed; estimates vary widely.

The revolution ended more than 250 years of Arab political domination of Zanzibar — from the Omani conquest of 1698 to the revolution of 1964.

What I find striking, having spent time in Stone Town: the revolution’s legacy is everywhere and nowhere at the same time. The People’s Palace (the renamed Sultan’s Palace) became a museum in 1994. The Revolutionary Council’s murals appear on walls. Karume’s name is on the airport — Abeid Amani Karume International Airport (ZNZ). But the layering of Arab, Indian, and British history in the stone and wood of the old town is so physically present that it insists on acknowledgement alongside the revolution that ended it. Zanzibar’s history is not a clean sequence. It is several histories, still living in the same square kilometre.

Union with Tanganyika: the making of Tanzania (April 1964)

Three months after the revolution, negotiations between Karume and Julius Nyerere — the first Prime Minister and then President of mainland Tanganyika (independent since December 9, 1961) — produced an agreement to merge the two countries.

On April 26, 1964, Tanganyika and Zanzibar formally united as the United Republic of Tanganyika and Zanzibar. The country was renamed the United Republic of Tanzania on October 29, 1964 — the name being a portmanteau of Tanganyika and Zanzibar.

Julius Nyerere became the first President of the United Republic. Abeid Karume remained as President of Zanzibar and Vice President of the Union until his assassination on April 7, 1972.

Zanzibar retains semi-autonomous status within Tanzania to this day. The Zanzibar Government (Serikali ya Zanzibar) has authority over all non-union matters — education, health, internal affairs, agriculture — with foreign policy, defence, and immigration handled at the union level. Zanzibar holds its own elections for its own president, and the relationship between the union government and the Zanzibar government has been a source of ongoing political tension throughout the post-independence period.

Stone Town’s UNESCO inscription and Freddie Mercury

In 2000, the Stone Town of Zanzibar was inscribed as UNESCO World Heritage Site #173. The inscription covers an area of 1.0 km² — the historic core of Zanzibar City as it developed primarily during the 19th century under Omani rule and British protectorate.

UNESCO recognised Stone Town under three criteria:

• Criterion (ii): an important interchange of human values over a significant period — specifically the sustained cultural exchange between Africa, Arabia, India, and Europe across the Indian Ocean trade network
• Criterion (iii): exceptional testimony to the Swahili coastal trading town tradition, with its distinctive architecture of coralline ragstone, mangrove timber, and carved wooden doors
• Criterion (vi): direct association with significant historical events — specifically the East African slave trade and its abolition

The Stone Town Conservation and Development Authority (STCDA) was established in 1985, fifteen years before the UNESCO inscription, and the town has been protected as a conservation area since that year.

One more historic fact worth knowing before you walk those alleys: Farrokh Bulsara was born in Stone Town on September 5, 1946. His family were Parsis who had moved from India to Zanzibar before his birth. He left at age 8 for boarding school at St. Peter’s School in Panchgani, India, and never returned to live in Zanzibar. He moved eventually to England, adopted the name Freddie Mercury, and became the lead singer of Queen. Mercury House in the alleys of Stone Town is now a recognised landmark — a modest building marking one of the stranger biographical footnotes in rock history: that one of the best-selling musicians of the 20th century grew up in the same UNESCO World Heritage trading city where, four centuries earlier, Portuguese navigators had expelled Arab merchants, and where, less than twenty years after Mercury’s birth, a revolution would dissolve the last sultanate of the Indian Ocean.

I’ve stood outside Mercury House and tried to hold all of that at once. The stone is still warm from the afternoon sun. The call to prayer starts somewhere two alleys over. A dhow is going somewhere in the channel. It doesn’t quite resolve, and I think that’s the honest response to Zanzibar’s history: not a neat summary, but a layered sensation of time that the place earns.

Where to go next

• Stone Town practical guide — how to spend half a day in the old town, what to see, and how to navigate the UNESCO alleys
• Zanzibar spice tour guide — the clove economy that built the Omani Sultanate, what a spice farm visit is actually like, and where to buy spices in Stone Town
• Zanzibar entry requirements — visas, Zanzibar Insurance (ZIC), and what you need before you land
• Zanzibar 7-day itinerary — a practical week in the archipelago, with Stone Town and history built into the schedule