exchange. Cultural achievements Several Rasulid sultans were culturally prominent, being men of letters who wrote literature and even treatises. Thus al-Afdal Abbas (r. 1363-1377) wrote an extensive compendium with passages about matters of practical utility, intellectual interest and entertainment, Fusul majmua fi'l-anwa' wa 'l-zuru' wa 'l-hisad. His son al-Ashraf Isma'il (r. 1377-1401) authored a general history of Yemen. Most of the rulers built mosques and madrasas, embellishing Ta'izz and other cities with fine buildings. Among the most well-known monuments are Jami al-Muzaffar from the thirteenth century and Ashrafiyya from the fourteenth century, both in Ta'izz. These monuments were inspired by models from places like Egypt and Syria and broke with the older Yemeni style of architecture. Coins were struck by all the sultans in the period c. 1236-1438. There were mints in several cities and the coins were characterized by symbols for each mint: fish for Aden, bird for Zabid, sitting man for Ta'izz, and lion for al-Mahjam. The fall of the Rasulids At length, however, they were unable to uphold the flourishing state constructed in the thirteenth century. A series of Zaidi imams managed to regain ground in the Yemeni highlands from the end of the thirteenth century, more importantly Zaidi imams managed to convert the Kurds of Dhamar (remnants of the Ayyubid military) into the Zaydi sect & pacified the Kurds of Dhamar, the Rasulid sultans were unable to score a decisive military success against rebels. Zaidi forces took Sanaa in 1324. The Mamluk sultans tended to increase their influence in Hijaz and the holy cities. In 1350 the Rasulid sultan al-Mujahid Ali was captured by Egyptian Mamluks in Mecca when he went on a pilgrimage, and was held prisoner in Egypt for a year. Sultan an-Nasir Ahmad (r. 1401-1424) was able to revive the Rasulid dynasty's declining fortunes and even received gifts from distant China. After his death in 1424 the dynasty fell into a period of upheaval and weakness, aggravated by the outbreak of the plague. Merchants from the east tended to bypass Aden due to the exactions and uncertainties there, going directly to Jedda in the Hijaz which was now part of the Egyptian Mamluk sphere of power. Unlike the previous pattern, when power struggles were only fought between the Rasulids themselves, various magnates interfered in the disputes during the last sultans. The most important of these magnates was the Tahir clan, which ruled Juban