Ṣa'da

Sadah is a walled city of the northern Yemeni highlands, on the inland route from Sanaa toward Najran. Its earth-built houses, markets and mosques stand within fortifications adapted to the plateau landscape. Before Islam the district was a station on the trade routes of southern Arabia; in the Islamic centuries Sadah became a centre of religious learning and political authority.

In 897 Yahya ibn al-Husayn, known as al-Hadi, established himself at Sadah and became imam. His teaching and his descendants' claims laid the foundations of the Zaydi imamate in Yemen. The mosque and mausoleum associated with him became enduring landmarks of the city; the dome of his tomb is considered among the earliest funerary domes in Yemen. Zaydi authority did not remain confined to Sadah. Rival imams and dynasties contested towns and strongholds across the highlands, and Ottoman armies entered Yemen in the sixteenth century. The city's place on the northern road and its association with the imamate ensured that it remained important in the struggles that shaped Yemen's later history.