Libraries before Islam were mainly private collections, not open to the public. When Muslims came, they improved upon existing libraries and introduced many concepts which are used in public libraries today.
Public libraries could be found in Musjids, homes and universities. In Aleppo, Syria, the Sufiya library contained 10,000 volumes. Ibn Nadim's bibliography shows the devotion of medieval Muslim scholars to books; it contains a description of thousands of books in the Islamic world around 1000 CE, when much of Europe was illiterate. Many books from early Islamic libraries were destroyed by Mongols, or taken to European libraries and museums in the colonial period. By the 9th century completely public libraries started to appear in many Islamic cities. In 10th century Iran the Muslim king set up a library of 360 rooms. In each department, catalogues were placed on a shelf. Some of these medieval libraries, like in Chinguetti, West Africa, remain intact and unchanged even today.
Many distinct features of the modern library were introduced in the Islamic world, where libraries not only served as a collection of manuscripts, but also as a public and lending library, a centre for the spread of sciences and a place for meetings. The library catalogue was also introduced in medieval Islamic libraries, where books were organized into specific categories. The contents of these Islamic libraries were copied by Christian monks in Muslim/Christian border areas, particularly Spain and Sicily. From there they made their way into other parts of Europe to form the basis of every modern library today.