Ibo Island lies at the southern end of the Quirimbas Archipelago, a string of 31 islands stretching more than 200 kilometres north to the Tanzanian border. The island was chosen by the Portuguese in 1754 as their main clearing house for slaves and ivory. Ibo Island is regarded as one of Africa's best-kept secrets.

Ibo Island is one of the most ancient settlements in Mozambique, after Ilha do Moçambique (usually just known as 'Ilha' in Mozambique). Its history dates back to at least the 1600 - Chinese grave stones still bear their readable dates, though Arab influence dates earlier.

As early as 600AD Arab traders had established contact with the local inhabitants and subsequently established fortified trading posts along the coastline where trading posts slaves, gold and ivory were shipped to the Arab world.

When the Portuguese arrived in the Quirimbas, the main trading centre in the archipelago was on the large Quirimbas Island (Next Island south of Ibo Island). In 1522, the Portuguese attacked Quirimbas Island because the trading Muslims of Quirimbas refused to trade with the Portuguese Christians. The town was therefore set alight and destroyed. 

By 1590 seven of the nine biggest islands were ruled by a Portuguese lord, and two by the Muslims.  Ibo Island traded in amber, jet, ivory, ambergris and turtle shell.  The locals had to pay 5% of their produce to the islands lord - as well as a contribution to the church. 

The Portuguese then built large rainwater cisterns that enabled them to raise cattle, pigs and goats in Ibo. Meat, millet, rice, beans and palm products were all exported and even Ilha de Mozambique seems to have been supplied from Ibo Island. By this time, Ibo Island had become the most important centre of the islands and in the mid 17th century the Archipelago was ruled by two main 'Mazumgo' (white) families - the Morues and the Meneses. Slave trade also became significant as the French needed labour for their plantations in Mauritius and Reunion. This trade brought more prosperity to Ibo even after the market switched to Brazil and later became illegal.  

In the late eighteenth century, Portuguese colonialists built the Fort of São João, which still survives, and the town, as a slave port, became the second most important in the region after Mozambique Island. Fort of São João Batista (St. John Baptist) was completed in 1791. The little chapel housed inside of the fort was built in 1795, followed by the Fort Santo Antonio (St. Anthony) and Fort of the Bairro de Rituto in 1847.

Throughout the 18th and 19th century the population of Ibo Island and the adjacent regions were consistently under attack from Dutch and Madagascar forces.  It wasn't until 1897, when Ibo Island was integrated into the administration of the Niassa Company that the island and population enjoyed relative safety and peace. In 1902 the capital District of Cabo Delgado was transferred from Ibo Island to Port Amelia, currently the city of Pemba, which remains the capital until today. This signaled the slow demise of the island, which eventually led to its total abandonment as a formal trading centre some years later. 

The Island has fine examples of 19th and 20th century Portuguese architecture. Ibo forms part of the Quiribas National Park. The island is accessible by dhow from Tandanyanga (about 150 kilometres north of Pemba) or by speedboat from Pemba.

References

http://www.iboisland.com/content1.cfm?AgentsID=279&PageID=324
http://www.go2africa.com/Mozambique/pemba-coast/ibo/
http://en.wikipedia.org/wiki/Ibo,_Mozambique