Levý Hradec was inhabited in the 7th century. In the 9th century the Przemyslids built a princely castle with fortifications. Prince Bořivoj, the first historically provable Czech Prince, was the ruler here. He originated the oldest church in Bohemia, the pre-Romanesque Rotunda of St. Clement, shortly after he was baptized at King Svatopluk in the Great Moravia. Therefore Levy Hradec is sometimes called the place of the beginning of Christianity in Bohemia.
In the year 982 Adalbert of Levý Hradec was elected the Prague Bishop. Every year the procession to Levý Hradec commemorates this event. The settlement was burnt down by Emperor Henry III and was never rebuilt. At the end of the 13th century the early Gothic presbytery was attached to the rotunda. In 1684 the old rotunda was put down and a new oblong nave and a spire were attached to the presbytery. Only the bases of the original rotunda have preserved below the recent Baroque nave, dated from the 17th century. The old bases with frescoes from the second half of the 14th century and Baroque tombstones were uncovered in 1940. In the church the main Baroque altar depicts St. Clement on the background of Levý Hradec. Another rarity is the Romanesque altar table with four legs made of four different sorts of wood.