LONDON — A letter from Catherine of Aragon pleading for help to preserve her marriage to King Henry VIII will be offered at auction in New York in December, Sotheby’s said yesterday.

The letter is part of an extraordinary batch of 31 documents owned by a collector whose identity was not disclosed.

Also up for auction is a handwritten document by Michelangelo Buonarroti about an important commission for a church in Rome, and items from composers Beethoven and Chopin, Soviet dictator Josef Stalin, and the 16-year-old Napoleon Bonaparte, the auctioneer said.

Catherine, the first of Henry’s six wives, wrote to her nephew, the Holy Roman Emperor Charles V, asking him to use his influence to persuade Pope Clement VII to resist Henry’s attempts to invalidate the marriage. The letter is dated February 8, 1534.

Clement’s rebuff of Henry led the monarch to reject papal authority, leading to the creation of the Church of England.

The letter has not been seen in public since it was sold at auction in New York in 1987 for $38,000. Sotheby’s estimated the price at the coming sale at $100,000 or more.

Sotheby’s said only one other autographed letter from Catherine had been sold since 1975.

Catherine, the youngest daughter of Queen Isabella and King Ferdinand of Spain, was previously married to Henry’s elder brother, Prince Arthur, who died six months after the marriage.

Catherine gave birth to a stillborn daughter, then to a boy who lived less than two months, before giving birth to a daughter who was to become Queen Mary. But Henry was desperate for a male heir, and came to believe — or assert — that Catherine’s failure to produce one was punishment for his sin in marrying his brother’s widow.

Henry pressed for an annulment when his lover, Anne Boleyn, became pregnant.

In her letter, Catherine told Charles, “There is no need for my relating to Your Highness the sufferings that I and my daughter undergo, as well in the treatment of our lives, as in the surprises and affronts which every day the King’s Council puts upon us, for our troubles are matters of universal notoriety …”

The Michelangelo letter, dated October 26, 1521, relates to final payments to two assistants for their work on the statue of the Risen Christ in the church of Santa Maria sopra Minerva in Rome. Commissioned by Metello Vari and Pietro Castellani, the work was executed in Rome and Florence between 1514 and 1520.

The letter confirms that Michelangelo, through the bank of Giovanni de’ Servihe, gave seven crowns and four “grossoni” to his agent, Leonardo Sellaio, to be paid to a Florentine sculptor named Frederigo and to Pierto Urbano of Pistoia.

Manuscripts by Michelangelo “are of the utmost rarity,” Sotheby’s said.