Francke was born in Lubeck in 1663 and had a talent for getting thrown out of places. His Pietist teaching - personal conversion, close Bible study, a Christianity of felt experience rather than doctrinal correctness - drew crowds and infuriated the Lutheran establishment. Leipzig banned him from lecturing in 1689. Erfurt made him a deacon in 1690 and gave him fifteen months before the civil authorities ordered him out of the city within forty-eight hours, on 27 September 1691. What saved him was a new university. Halle was being organised from scratch, Philipp Jakob Spener spoke for him, and in December 1691 Francke arrived with a chair at the university and the pastorate of Glaucha, a poor suburb outside the town wall. He began giving to the poor on Thursdays, the town's alms day, and quickly concluded that charity without schooling changed nothing.

The poor school opened in 1695, taught by university students. It worked well enough that paying families started asking to send their children too, so Francke added the Paedagogium for the sons of the nobility and merchant class, then a Latin school in 1697. In 1698 he began the orphanage, finished around 1701 and startlingly grand for its purpose - a huge half-timbered block whose tympanum carries two eagles rising towards the sun and a line from Isaiah about those who wait on the Lord rising up with eagles' wings. He built it with no capital and no state patronage, on money that arrived as fast as the workmen had to be paid and never faster. Baron von Canstein visited in 1706 and described the place to a Prussian official as a kind of little world, all in harmony and in a state of great efficiency. By 1698 there were a hundred orphans and five hundred day pupils. By Francke's death in 1727, more than 2,300.

Faith kept the accounts, but enterprise kept the doors open. A chemist left Francke a medicine recipe, and the resulting apothecary became a substantial and long-running income. In 1711, with Carl Hildebrand von Canstein, he founded the Cansteinsche Bibelanstalt - the oldest Bible institute in Germany and effectively the first modern Bible society - which used standing type to print scripture in enormous runs at prices ordinary people could afford, and went on producing them into the twentieth century. The Foundations also became the hub of the Danish-Halle Mission, sending the first Protestant missionaries to India and building a correspondence network that carried Halle's ideas about schooling to Russia, North America and the Indian coast. Contemporaries started calling the place the New Jerusalem, which was meant admiringly and does convey the ambition.

Two rooms explain the intellectual project better than any description of it. Up in the attic of the orphanage sits the Kunst- und Naturalienkammer, a cabinet of artefacts and curiosities that is among the oldest teaching collections in Germany, restored to its eighteenth-century arrangement: eighteen carved cabinets holding about 3,000 objects, the natural specimens sorted into stones, plants and animals, the made things into fine art, writing, coins, dress and daily life. Children were meant to learn from looking. The historic library, in its own purpose-built house from 1728, holds around 50,000 volumes and keeps its original fittings entirely - shelving arranged like stage scenery, restored between 1996 and 1998 to its appearance of 1746. Standing in it is the closest most people will come to seeing what a working Enlightenment library actually looked like.

The twentieth century nearly finished it. In 1946 the provincial authorities abolished the Foundations and transferred the assets to Martin Luther University; the complex became state property, and in the 1970s part of the orphanage's northern wall was pulled down for a road. Buildings rotted quietly for four decades. Restoration began in 1991 and the Foundations were re-established as a public-law foundation in 1992, and what has come back is not a museum. More than 4,000 people now learn, teach, work and live inside the walls: three kindergartens, four schools including the Latina that descends directly from Francke's 1697 foundation, a children's creative centre, a house that puts a Montessori primary school and a care home under one roof, research institutes on Pietism and the Enlightenment, and the German Federal Cultural Foundation. It has been on Germany's UNESCO nomination list since 1999.