The Portuguese expeditionary force, led by Prince Henry the Navigator, Duke of Viseu, set out from Portugal in August 1437, intending to seize a series of Moroccan coastal citadels.

After a few failed assaults on the city, the Portuguese force was attacked and defeated by a large Moroccan relief army led by vizier Abu Zakariya Yahya al-Wattasi of Fez.

Simultaneously, it was an enormous boon to the political fortunes of the vizier Abu Zakariya Yahya al-Wattasi, who was transformed overnight from an unpopular regent to a national hero, allowing him to consolidate his power over Morocco.

In 1432, Henry the Navigator proposed to his father King John I of Portugal an ambitious project to allow him to lead a war of conquest of Marinid Morocco, or at least carve out a wider regional enclave in the north.

[10]) In defense of the project, Henry pointed out the Marinid kingdom of Morocco was deeply fractured among rebellious lords and the leadership in Fez was embroiled in political crisis.

The young Marinid sultan Abd al-Haqq II was coming of age, but his unpopular Wattasid vizier (and regent since 1420), Abu Zakariya Yahya al-Wattasi, refused to yield power.

Henry also believed the manpower concerns were exaggerated, that it would be sufficient to seize and hold the critical ports of Tangier, Ksar es-Seghir, and Asilah, to exert Portuguese dominance over all of northern Morocco, and that should the pope give the campaign the privileges of a crusade, soldiers from all over Portugal and Christian Europe would rally to enlist and fill in the gap.

Henry soon obtained a critical ally, his youngest brother Prince Ferdinand, who was dissatisfied with his meager estates in Portugal and eager to seek his fortune overseas.

[23] According to chronicler Ruy de Pina, Edward 'forgot' to summon the dissenting brothers – Peter of Coimbra, John of Reguengos, and Afonso of Barcelos – to the Evora parliament.

[26] This bore fruit in September, when Pope Eugenius IV issued the bull Rex Regnum blessing the Tangiers enterprise with the privileges of a crusade.

The same month (September), Pope Eugenius IV issued another bull at Henry's request, Romanus Pontifex, granting Portugal the right to subjugate the unconquered part of the Canary Islands.

The Castilian prelate Alfonso de Cartagena, Bishop of Burgos, then attending the Council of Basel, launched a legal offensive, supplying volumes of documents proving that all of the Canaries rightfully belonged to Castile.

[31] While it is probable that Cartagena was only half-serious, and sought merely to rattle Henry, the sudden splurge of Castilian claims nearly sank the Tangier expedition, and opened alarm at the prospect of a new war between Portugal and Castile.

His experienced nephew Ferdinand (Count of Arraiolos) (who earlier pronounced himself against the expedition) was appointed constable of the nobles and sent to Porto to organize the embarcation of troops from northern Portugal.

The Portuguese chroniclers, with probable exaggeration, claim it was composed of 10,000 horsemen and 90,000 foot[60] Henry moved his army to a hillside, offering battle, but the Moroccans just held their position in the valley.

After three motionless hours, Henry ordered the Portuguese to march against them and force the issue, but the Moroccans just retreated back up the hills, evidently wishing to hold the higher ground.

[68] On October 9, Henry was preparing his third assault when he received intelligence of a new massive Moroccan relief army – reported (with doubtless exaggeration) to be some 6000 horse and 7000 foot.

[69] This army was led by Abu Zakariya Yahya al-Wattasi (Lazeraque), the vizier of the Marinid sultan Abd al-Haqq II of Fez (whom the chroniclers suggest was present).

It is said that Henry was alone on foot for a while, surrounded by Moroccan cavalry, and saved only by the heroics and personal sacrifice of Fernão Alvares Cabral and a group of his guards who rushed in to extract him.

[77] Chronicler Frei João Álvares reports that at this point, the Portuguese expeditionary force in the siege camp was a mere 3,000, implying that of the original 7,000 who arrived at Tangier, 4,000 or so had died or deserted.

Chronicler Ruy de Pina reports that, on October 12, having taken many casualties, Abu Zakariya called off further assaults on the camp and decided to open communications to the Portuguese defenders, offering to make peace in return for Ceuta.

With the tacit permission of the Moroccan leaders, in an overnight operation on Saturday evening, Henry had his men reduce the circumference of the siege camp (and shift it slightly closer to the sea), allowing the Portuguese to defend themselves more effectively against renegade skirmishers.

A little earlier, sometime in September, the constable John of Reguengos had traveled to the southern province of the Algarve to raise more troops and organize the dispatch of reinforcements and supplies to Henry in Tangier.

In June, no longer able to resist his brother's summons, Prince Henry left Ceuta and returned to Portugal, but he requested exemption from presenting himself in the king's court in Evora.

The flotilla went out in a celebratory mood – the ambitious Fernando de Castro openly fantasized that the released Infante Ferdinand might be persuaded to marry his own daughter on the spot, and prepared a rich and well-stocked expedition, packing the ships with banquet finery, an entourage of notables, and a bodyguard of some 1,200 troops, but on the outward journey, around Cape Saint Vincent, the Portuguese flotilla was ambushed by Genoese pirates.

[117] Arriving in Fez in May, the emissaries presented the vizier Abu Zakariya with sealed letters from Peter of Coimbra confirming Noronha's dismissal and a copy of the royal instructions given to Castro to evacuate Ceuta.

[119] The detention of Master Joseph (which lasted until September) gave Abu Zakariya time to assemble a Moroccan army for a triumphal march to Ceuta, intending to garrison the citadel as soon as it was evacuated.

It is uncertain what else the emissary reported about Abu Zakariya's intentions, but the Portuguese ambassadors rejected the offer, arguing they were not prepared to "hock Ceuta for paper promises",[120] that they needed to have some sort of hold on Ferdinand's person.

The Saint Vincent Panels, painted by Nuno Gonçalves around this time, is believed by some art historians to represent such a political statement, a funerary homage to Ferdinand the Holy Prince, pointing an accusatory finger at Henry the Navigator.

The victory of Tangier dramatically changed the political fortunes of the unpopular Abu Zakariya Yahya al-Wattasi, vizier of the Marinid palace of Fez and regent for sultan Abd al-Haqq II.