Barka, are only mentioned by the 15th-century Persian author Muʿīn-ad-Dīn Naṭanzī, who is often confused about the history of the Golden Horde); it certainly cannot be identified with "New Sarai", which was founded more than six decades after Berke's death. The earliest coins struck at Sarai have been identified with issues of Berke from 1264/1265. During the reign of Mengu-Timur Khan silver coins (dirhams) were again struck with the label "Sarai" in 1272/1273; coins of more consistent standard and issue followed under Toqta Khan, especially after 1310. New Sarai "New Sarai" (Sarāy al-Jadīd) is said to have been founded or formally inaugurated by Öz Beg Khan in the first half of the 14th century. The earliest explicit reference to a city bearing this name is the notice of the death of Öz Beg in "New Sarai" in March–April 1341 by a nearly contemporary Mamluk author. A statement of the Timurid historian Ibn ʿArabshāh that "between the building of Sarāy and its devastation there passed sixty-three years" would place the formal founding of "New Saray" 63 lunar years before its sack by Timur in the winter of 1395–1396, and so in 1334–1335. The reasons for the relocation of the capital are unclear, as is how substantial such a relocation actually was (since identifications of sites of "Old Sarai" and "New Sarai" are debated), although it is sometimes assumed that the rationale was a change in the level of the Caspian Sea and the extent of the waterways in the Volga Delta. Sarai and the other major centers of the Golden Horde (like Gülistan, preferred by Jani Beg) along the lower Volga benefited from trade and exhibited a significant degree of cultural prosperity. While the origin of coins simply labeled "Sarai" remains uncertain, coins labeled "New Sarai" started to be minted from 1342. An astrolabe was discovered during excavations at the site, and the city was home to many poets, most of whom are known only by name. These included Hisām Kātib (c. 1375)and Sayf-i Sarāy, who died in 1396. This prosperity was rapidly threatened by the onset of chronic political and military instability alongside competition for the throne of the Golden Horde after 1361. As the traditional capital and a rich and prestigious prize, Sarai became the target of most claimants to the throne. The beglerbeg Mamai, for example, took Sarai on behalf of his own puppet khans on four or