You will be given a definition of a task first, then some input of the task.
This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

With the union of the crowns of Castille and Aragon (1479), the use of Spanish gradually became more prestigious. Starting in the 16th century, Catalan literature experienced a decline, the language came under the influence of Spanish, and the urban and literary classes became bilingual.
Output:
When were Castille and Aragon united?