by periodic tribal revolts, as they were locked in a war of attrition with the Zaydi imams in the northern highlands. During the last twelve years of Rasulid rule, the country was torn between several contenders for the kingdom. The weakening of the Rasulids provided an opportunity for the Banu Taher clan to take over and establish themselves as the new rulers of Yemen in 1454. Tahirid Dynasty The Tahirids were a local clan based in Rada'a. While they were not as impressive as their predecessors, they were still keen builders. They built schools, mosques and irrigation channels as well as water cisterns and bridges in Zabid and Aden, Rada'a, and Juban. Their best-known monument is the Amiriya Madrasa in Rada' which was built in 1504. The Tahiride were too weak either to contain the Zaydi Imams or to defend themselves against foreign attacks. The Mamluks of Egypt tried to attach Yemen to Egypt and the Portuguese, led by Afonso de Albuquerque, occupied Socotra and launched an unsuccessful four-day siege of Aden in 1513. The Portuguese posed an immediate threat to the Indian Ocean trade; the Mamluks of Egypt therefore sent an army under the command of Hussein Al-Kurdi to fight the intruders. The Mamluk sultan of Egypt sailed to Zabid in 1515 and began diplomatic talks with Tahiride Sultan 'Amir bin Abdulwahab for money that would be needed for jihad against the Portuguese. Instead of confronting the Portuguese, the Mamluks, who were running out of food and water, landed their fleet on the Yemen coastline and started to harass Tihama villagers for what they needed. Realizing how rich the Tahiride realm was, they decided to conquer it. The Mamluk army with the support of forces loyal to Zaydi Imam Al-Mutawakkil Yahya Sharaf ad-Din conquered the entire realm of the Tahiride but failed to capture Aden in 1517. The Mamluk victory turned out to be short-lived. The Ottoman Empire conquered Egypt, hanging the last Mamluk Sultan in Cairo. It was not until 1538 that the Ottomans decided to conquer Yemen. The Zaydi Highland tribes emerged as national heroes by offering a stiff, vigorous resistance to the Turkish occupation. Modern history The Zaydis and Ottomans The Ottomans had two fundamental interests to safeguard in Yemen: The Islamic holy cities of Mecca and Medina and the trade route with India in spices and textiles, both of which were threatened and the latter