William of Rubruck, who visited the Mongol Empire between 1253 and 1255, listed Michael's realms ("Blakia—Assan's territory—and Little Bulgaria") among the countries paying tribute to the Mongols.
Willem van Ruysbroeck, yang mengunjungi Kekaisaran Mongol antara 1253 dan 1255, mendaftarkan wilayah Mikhail ("Blakia—wilayah Assan—dan Bulgaria Kecil") di antara negara-negara yang memberi penghormatan kepada bangsa Mongol.