Friction began early, after the Cape Verdes had been passed; probably following Portuguese roteiros, Magellan kept on a southerly course instead of striking across the Atlantic, and this may well have alarmed the Spanish officers: was the Captain-General luring them into Portuguese waters? Juan de Cartagena was plainly insolent and insubordinate, garbling and then omitting the regulation evening greetings to the commander, and at a suitable opportunity Magellan deprived him of his captaincy of the San Antonio and put him under arrest. So matters stood as the fleet passed across to Brazil and, in January 1520, explored the La Plata estuary. Hopes were raised by this great opening, but there was no passage either here or in the Gulf of San Matias further south, and on 31 March Magellan reached Puerto San Julian, in 49°20′S, where he decided to winter. Here, faced with a long wait on reduced rations in a cold climate, discontent broke into open mutiny, and an officers’ mutiny at that.

Representations, more or less mutinous, demanding a return were very common from crews wintering in high latitudes. Magellan succeeded in talking down the desire of the seamen to turn back, partly by pointing out that things would be much easier in the spring and that wood, water, fish and birds were plentiful, so that rations could be supplemented; partly by an appeal to pride; most of all, perhaps, by driving leadership: he himself was determined to find a passage, as far south as 75° if need be, or to die. The sedition of the officers was far more serious.

At Easter,^[47] only one of the captains—Magellan's cousin Alvaro de Mesquita, now in command of the San Antonio—accepted his invitation to Mass and a feast on the flagship. During the night the conspirators, led by Juan de Cartagena- 44 -and Gaspar de Quesada, took over the San Antonio, Victoria, and Concepcion. Next morning there were negotiations, probably of doubtful sincerity on either part; Magellan sent a small party with concealed arms to the Victoria, ostensibly to arrange a conference; her captain Luis de Mendoza was stabbed without warning, and the ship seized, to join with the loyal Trinidad and Santiago in blocking the harbour mouth. At night the San Antonio made a feeble attempt to break out, but the swift retaking of the Victoria had taken the heart out of the mutineers. After their surrender Alvaro de Mesquita presided over a court, which sentenced forty men to death, including Juan Sebastian del Cano, whom the rebels had put in command of the San Antonio. Obviously this sentence on well over a sixth of the complement was a formality; in the event only Quesada was beheaded and quartered, as was the body of Mendoza. Juan de Cartagena was not executed, probably because of his royal commission, but sentenced (perhaps after a second attempt to stir up revolt) to be marooned.

There can be no doubt at all that Magellan had contributed very greatly to the outbreak by his overbearing manner, secretiveness, and partiality for Portuguese officers. That said, and considering the stakes, he can hardly be blamed for meeting rebellion with ruthlessness and little scruple. Mutiny was a constant nightmare of exploring captains until well into the eighteenth century; and unless the commander struck at once and hard, the voyage was doomed; a century later Richard Hawkins was to write

It was in effect on suspicion of projected mutiny that Drake executed Thomas Doughty in this very Puerto San Julian; and here his people found the remains of what they took to be a gibbet ‘with men's bones underneath it’, a grim memento of the bloody Eastertide nearly sixty years earlier.^[49]

During the winter the little Santiago was lost on a reconnaissance to the south, but the crew was able to make its way back to San Julian; contact was made with the inhabitants, to the delight of Pigafetta (who had the instincts of an anthropologist) and the tale of the Patagonian (‘big feet’) giants was launched on its long history. Perhaps fearing the results of long inaction in this port of evil memories, Magellan took the four remaining ships to sea in late August, leaving behind Juan de Cartagena and an accomplice, with wine and some bags of biscuit.

Ten degrees farther south the fleet spent two months at the Rio Santa Cruz, taking on wood, water, and fish. With spring, they put to sea again, and four days later, in about 52°30′S, they saw on 21 October, St Ursula's Day, a cape which they named for her Eleven Thousand Virgins, and beyond it ‘certain inlets of the sea … which had the appearance of a strait.’