In 1592, a squadron of the Royal Navy attacked a Portuguese fleet and drove one ship, the Santa Cruz, aground. Although the Portuguese had reclaimed much of the cargo of that ship, the English did compel (i.e. threatened to torture) some of the survivors to reveal that another group of ships was following them. The raiders lay waiting for them to arrive.
In mid-August, they sighted, attacked, and, after a day-long battle, seized one of these ships. I imagine that it was clear right away that this was no ordinary ship.
This was the Madre de Deus, an enormous Portuguese carack. It was over 160’ long, 47’ wide, weighed some 1600 tons, of which 900 tons was cargo, and had a gilded superstructure. It had a crew of something over 600 men, covered 7 decks, and carried 32 guns. In all, it was some three times the size of the largest ship then in the Royal Navy - the great ships like the Mary Rose and the Henry Grace à Dieu having sunk - this ship must have been very imposing indeed. But of particular interest to the English raiders was its cargo.
According to Wikipedia, the inventory reports:
… the following goods aboard, besides jewels: "spices, drugs, silks, calicos, quilts, carpets and colors, &c. The spices were pepper, cloves, maces, nutmegs, cinnamon, greene, ginger: the drugs were benjamin, frankincense, galingale, mirabilis, aloes zocotrina, camphire: the silks, damasks, taffatas, scarceness, alto bassos, that is, counterfeit, cloth of gold, unwrought China silk, sleeved silk, white twisted silk, curled cypresse. The calicos were book-calicos, calico-launes, broad white calicos, fine starched calicoes, course white calicos, brown broad calicos, brown course calicos. There were also canopies, and course diapertowels, quilts of course sarcenet and of calico, carpets like those of Turky; whereunto are to be added the pearl, muske, civet, and amber-griece. The rest of the wares were many in number, but less in value; as elephants teeth, porcellan vessels of China, coco-nuts, hides, ebenwood as black as jet, bested of the same, cloth of the rind’s of trees very strange for the matter, and artificial in workmanship".
In all, it was estimated that the cargo was worth some half a million pounds, almost half the value of the entire English treasury. That number doesn’t seem terribly large, but if we were to imagine 3% inflation over the intervening 400 years we would have a value of something over 60,000,000,000 pounds. It was, quite literally, a king’s ransom. But not all of it reached the crown: the sailors in the raid had already started stuffing their pockets with the treasure, and when it reached England it attracted all manner of thieves with even the local fishermen making night-time visits to the ship. By the time Walter Raleigh was sent to restore order, perhaps two thirds had vanished. The English had learned their lesson – in the future the dockworkers would have to wear "suits of canvas doublet without pockets".
Among all those obvious treasures was one less gaudy but no less valuable: a document detailing Portuguese trade in China and Japan. This was a critical find, the money on the ship may be lost or squandered, but with this information the English could kick-start their own trade in the east. Again from the inventory at the time:
"Gods great favor towards our nation, who by putting this purchase into our hands hath manifestly discovered those secret trades & Indian riches, which hitherto lay strangely hidden, and cunningly concealed from us".
Raids like this really underline just how much wealth must have been coming back into Europe from the New World. Here is a ship carrying the kind of wealth that nations formerly could only dream of (outside of, perhaps, the Papacy), sailing across the ocean largely undefended. Did the Spanish and Portuguese treat these raids the way that a department store treats shop-lifting: as long as the losses are only a small fraction of the total takings it’s not worth trying to prevent them?
In a fantasy setting, especially one with a high-magic feel, just what kind of protection would a ship like this have to be carrying? Would it be bristling with wizards or magical defences? Or would there simply be too much danger in sending single large ships, that the treasure would have to come across in many smaller ones instead?
And what about those documents, would your players think to themselves, “Oooh, someone will pay well for these”? Would they even know who to take it to?