Bukhara eclipsed Samarkand in the 16th century. Being an oasis surrounded by a large desert, an irrigation system based on many pools and canals was established and is still evident in the city. The center of old Bukhara is a the Lyabi Hauz square, built around a large pool and surrounded by three ancient madrassas. The old city is full of ancient madrassas, caravanserai and covered markets. The outstanding Kalon minaret, main mosque and old fortress add to the attraction. Lyabi-Hauz (in Tajik 'around the pool') is Bukhara's peaceful central plaza Nadir Divanbegi, the khan's grand vizier, in about 1620 wanted to build a reservoir in the centre of Bukhara on the site the house of an old woman. When she refused to move he had a canal built below the house, undermining its mud foundations and forcing her to leave. So he then built the reservoir.The beautiful pool is that reservoir. Around it are the Nadi Divanbegi madrasa and khanaga, both dating back to 1620. The madrasa was intended to be a caravanserai, but when he inaugurated it the khan made a mistake and called it a madrasa. Nothing said by him could be undone, so it was converted into a madrasa.