Beginning with Selim I's acquisition of Medina and Mecca in 1517, the Ottomans, in the 16th century, added to their Empire the Hejaz and Asir regions along the Red Sea and the al-Hasa region on the Persian Gulf coast, these being the most populous parts of what was to become Saudi Arabia. They also laid claim to the interior, although this remained a rather nominal suzerainty. The degree of control over these lands varied over the next four centuries with the fluctuating strength or weakness of the Empire's central authority. In the Hejaz, the Sharifs of Mecca were largely left in control of their territory (although there would often be an Ottoman governor and garrison in Mecca). On the eastern side of the country, the Ottomans lost control of the al-Hasa region to Arab tribes in the 17th century but regained it again in the 19th century. Throughout the period, the interior remained under the rule of a large number of petty tribal rulers in much the same way as it had in previous centuries.