Was the story of Orys and Argella the inspiration for the wedding and bedding ceremonies of Westeros, or did those customs exist before the invasion of Aegon the Conqueror?
It’s an interesting question. The story of Orys Baratheon and Argella Durrandon does bear some resemblance to Westeros’s wedding traditions. As I’m sure you know, the story goes that during Aegon’s War of Conquest, his Hand Orys was sent to capture the Stormlands; and in the battle called the Last Storm, Orys defeated King Argilac Durrandon’s army, and the king himself in single combat. Afterwards:
For a few days it was feared that Storm’s End might suffer the same fate as Harrenhal, for Argilac’s daughter Argella barred her gates at the approach of Orys Baratheon and the Targaryen host, and declared herself the Storm Queen. Rather than bend the knee, the defenders of Storm’s End would die to the last man, she promised when Queen Rhaenys flew Meraxes into the castle to parley. “You may take my castle, but you will win only bones and blood and ashes,” she announced… but the soldiers of the garrison proved less eager to die. That night they raised a peace banner, threw open the castle gate, and delivered Lady Argella gagged, chained, and naked to the camp of Orys Baratheon.It is said that Baratheon unchained her with his own hands, wrapped his cloak around her, poured her wine, and spoke to her gently, telling her of her father’s courage and the manner of his death. And afterward, to honor the fallen king, he took the arms and words of the Durrandon for his own. The crowned stag became his sigil, Storm’s End became his seat, and Lady Argella his wife.
–The World of Ice and Fire
But despite some of the similarities – the cloak of protection, the nudity, etc – I think the answer to this question is in the age and location of the event. Aegon’s Conquest was only 300 years ago, and this event took place in the Stormlands. Whereas the cloaking ceremony is part of all of the wedding traditions of Westeros – Andal and First Men, Faith of the Seven and Old Gods and even R’hllor. Something that widespread among all the various peoples and cultures of Westeros suggests an ancient ceremony, most likely something that came to Westeros with the First Men thousands of years ago and spread throughout the continent following the lines of immigration, and was kept as a tradition even with the influx of the Andals and the additional ceremonies of their Faith. Aegon’s Conquest and the Targaryens were very influential, but not that culturally influential, not that pervasive, not that quickly.
Also, the fact that Orys took Argella’s sigil as his own – as opposed to weddings where the bride’s family’s sigil is replaced by that of her husband’s – is a key difference, and further proof that the wedding traditions of Westeros were not based on this event. But I’m sure the similarities are there for a reason. First, by the author, as a sign that we’re supposed to look at the interaction of Orys and Argella as a romantic scene. But also in-world, in the sense that singers most likely wrote of the event as a symbolic marriage for the couple that was sealed by their true marriage not long afterwards.
Thanks for the question, and I hope this answer satisfies!