Francis I of France had continued his policy of seeking a middle course in the religious rift in France until an incident called the Affair of the Placards.  The Affair of the Placards began in 1534, and started with protesters putting up anti-Catholic posters. The posters were not Lutheran but were Zwinglian or "Sacramentarian" in the extreme nature of the anti-Catholic content—specifically, the absolute rejection of the Catholic doctrine of "Real Presence."  Protestantism became identified as "a religion of rebels," helping the Catholic Church to more easily define Protestantism as heresy. In the wake of the posters, the French monarchy took a harder stand against the protesters. Francis had been severely criticized for his initial tolerance towards Protestants, and now was encouraged to repress them.  At the same time, Francis was working on a policy of alliance with the Ottoman Empire.  The ambassadors in the 1534 Ottoman embassy to France accompanied Francis to Paris.  They attended the execution by burning at the stake of those caught for the Affair of the Placards, on 21 January 1535, in front of the Cathedral of Notre-Dame de Paris. John Calvin, a Frenchman, escaped from the persecution to Basle, Switzerland, where he published the Institutes of the Christian Religion in 1536. In the same year, he visited Geneva, but was forced out for trying to reform the church. When he returned by invitation in 1541, he wrote the Ecclesiastical ordinances, the constitution for a Genevan church, which was passed by the council of Geneva.. How many years after being forced out, did John Calvin return to Geneva by invitation?