At an early age, Catherine was considered a suitable wife for Arthur, Prince of Wales, the eldest son of Henry VII of England and heir to the throne, due to the English ancestry she inherited from her mother Queen Isabella I of Castile. By means of her mother, Catherine had a stronger legitimate claim to the English throne than King Henry VII himself through the first two wives of John of Gaunt, 1st Duke of Lancaster: Blanche of Lancaster and the Spanish Infanta Constance of Castile. In contrast, Henry VII was the descendant of Gaunt's third marriage to Katherine Swynford, whose children were born out of wedlock and only legitimised after the death of Constance and the marriage of John to Katherine. The children of John and Katherine, while legitimised, were barred from ever inheriting the English throne, a stricture that was ignored in later generations. Because of Henry's descent through illegitimate children barred from succession to the English throne, the Tudor monarchy was not accepted by all European kingdoms. At the time, the house of Trastámara was the most prestigious in Europe, due to the rule of the Catholic Monarchs, so the alliance of Catherine and Arthur validated the House of Tudor in the eyes of European royalty and also strengthened the Tudor claim to the English throne via Catherine of Aragon's ancestry. It would also have given a male heir an indisputable claim to the throne.
For two years, Arthur wrote numerous letters in Latin to his bride-to-be, and she would formally reply. However, as the young couple had never met, the letters were written as instructed by their tutors and were more polite than passionate.
The two were married by proxy on 19 May 1499 and corresponded in Latin until Arthur turned fifteen, when it was decided that they were old enough to be married.
When Arthur was 14, Ferdinand of Aragon and Isabella of Castile promised to send their daughter Catalina (later known as Catherine) to England, but it was not until after Arthur turned 15 that Catherine and her retinue finally started their journey. The Spanish Infanta finally landed in the autumn, and on 4 November 1501, the couple met at last at Dogmersfield in Hampshire.
When Catherine of Aragon travelled to London she brought a group of her African attendants with her, including one identified as the trumpeter John Blanke. They are the first recorded Africans to arrive in London at the time, and were considered luxury servants. They caused a great impression about the princess and the power of her family.
Little is known about their first impressions of each other, but Arthur did write to his parents in law that he would be "a true and loving husband" and he later told his parents that he was immensely happy to behold the face of his lovely bride. Unfortunately, the couple found that they could not understand each other, since they had learned different pronunciations of Latin. Ten days later, on 14 November 1501, they were married at Old St Paul's Cathedral. At the end of the festive day came the bedding ceremony, in which most of the court put the young couple to bed.
The couple soon travelled to Ludlow Castle on the Welsh border, where Arthur resided in his capacity as Prince of Wales and President of The Council of Wales and Marches. He died suddenly at the early age of 15. The cause of his death is unknown.
Catherine also fell ill, but survived. Arthur's brother, Henry, Duke of York, was not created Prince of Wales until it was certain Catherine wasn't carrying Arthur's child. She lived in relative obscurity until becoming Henry's first wife after his coronation.
Henry became heir upon Arthur's death and would come to the throne in 1509.