CNN, The State Department on Thursday released its annual report on global terrorist activity, listing Iran as the top state sponsor of terrorism and labeling ISIS "the greatest threat globally." The report also includes statistics on terrorist activity worldwide, and said 11,774 terrorist attacks in 92 countries occurred in 2015. Iran is an Islamic republic on the Persian (Arabian) Gulf with historical sites dating to the Persian Empire. Extensive marble ruins mark Persepolis, the empire’s capital founded by Darius I in the 6th century B.C. The modern capital, Tehran, is home to opulent Golestan Palace, seat of the Qajar Dynasty (1794–1925), plus modern landmarks such as the 435m-high Milad Tower.