In the summer of 1516, it was evident to most observers of the Ottoman imperial palace of Topkapi in Istanbul, if not to most residents of the city at large, that Sultan Selim I (1512–20) was preparing a decisive military expedition against one of his two chief Asian antagonists. Early in the season, the sultan's campaign tent had been pitched at Üsküdar, on the eastern shore of the Bosphorus; by July, he had reached the camp of his general Sinan Pasha in the eastern Anatolian town of Malatya. Up to this point, however, which rival Selim intended to attack remained open to question. The militantly Shiʿite Safavid empire, which had swept across Iran early in the sixteenth century, posed a sharp political and ideological challenge to the Ottoman Empire. Only two years earlier, in fact, Selim had dealt the Safavids a bruising defeat at Chaldiran in northwestern Iran. It was to pursue the campaign against the Safavids that Sinan Pasha had marched to Malatya. To the south, however, the Mamluk sultans, who ruled Egypt, Syria, the Hijaz, and southeastern Anatolia, had become a major irritant to Selim. Although they, like the Ottomans, were Sunni Muslims, they refused to support the Ottoman effort against the Safavids. They were also a poor buffer against the Portuguese presence in the Red Sea and Indian Ocean. Diplomatic relations between the Ottomans and Mamluks had deteriorated in recent months. Two Ottoman ambassadors to the Mamluk court at Cairo had been humiliated and abused.