Ibrahim ibn Yaqub (fl. 961–62; sometimes Ibrâhîm ibn Ya`qûb al-Tartushi or al-Ṭurṭûshî; also Abraham ben Jacob) was a 10th-century Hispano-Arabic, Sephardi Jewish traveller, probably a merchant, who may have also engaged in diplomacy and espionage. His family hailed from Moorish-ruled Ṭurṭūšah (now Tortosa) close to the mouth of the Ebro: he may also have lived in Cordova. Written and oral history and his writings suggest that he had a Jewish background. However, it has also been argued by other historians that he was a Muslim of Jewish background, and Bernard Lewis states: "There is some uncertainty to whether he was a professing Jew or a Muslim of Jewish origin." In 961–62 he travelled in Western and Central Europe and in Italy at least as far as Rome, where he was received with an audience with the Holy Roman Emperor Otto I during the first week of February. Nothing is known about his return to 'al-Andalus' (the Muslim-ruled part of the Iberian Peninsula), nor of any further travel. The memoirs and commentaries of his journey, possibly first presented to the Cordovan caliph Al-Hakam II (961–76), have been lost; only excerpts by later authors have been preserved, i.e., in Abu Abdullah al-Bakri's Book of Highways and of Kingdoms. His work is widely known as providing the first reliable description of the Polish state under Mieszko I, the first historical ruler of Poland. He is also noted for his description of the Vikings living in Hedeby, of the Nakonid fortification at Mecklenburg Castle and of what was, in all likelihood, the nucleus of the later ducal castle and palace at Schwerin. Ibrahim ibn Yaqub has a unique place in Czech history as the first person to mention the city of Prague in writing. He is also mentioning Czech Boleslaus I, Duke of Bohemia and Krakow as part of Duchy of Bohemia.