Saudi Arabia is barring international visitors for the hajj. A scholar explains a long history of disease, politics and war that have previously prevented people from making the journey to Mecca.
The Islamic State has appointed yet another 'caliph' after the death of Abu Bakr al-Baghdadi. What is the idea behind the caliphate?
There have been several attacks on Shia mosques in several parts of the world. At its heart is the centuries'-old sectarian Shia-Sunni divide.