In the year 570 A.D., the Prophet Muhammad was born in Mecca.  In 628, the Persian Governor of Yemen converted to Islam and the whole of the people soon followed.  The first mosques were built in Yemen during his lifetime, in Sana'a, Al-Janad and Zabid.  After Muhammad's death in 632, the Yemenis sent more than 20,000 troops to fight alongside the new Caliph in Islam, Abu Bakr as-Siddiq.  Yemen was then divided into three provinces, Sana'a, Al-Janad and Hadramawt.

In 819, Muhammad ibn Ziyad founded an empire which lasted for two hundred years, whose capital, Zabid, lasted far longer as a center for Sunni learning.  The Zaydis next took up the mantle of power in southern Arabia in 897 and founded a sect of Shi'a Islam which many still practice today in Yemen. 

The famous minaret of Tarim, Hadramawt, the tallest in Yemen.

Minarets like these cover Yemen from north to south.