You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Martin_Luther

Context:
In October 1529, Philip I, Landgrave of Hesse, convoked an assembly of German and Swiss theologians at the Marburg Colloquy, to establish doctrinal unity in the emerging Protestant states. Agreement was achieved on fourteen points out of fifteen, the exception being the nature of the Eucharist – the sacrament of the Lord's Supper—an issue crucial to Luther.

Question:
When did Philip I convene an assembly to set doctrine in the Protestant states?

October 1529