The largest historical square in Prague was established by Charles VI in 1348 in connection with the foundation of Prague’s New Town. Among the oldest buildings on the square are the New Town Hall building, dating back to the time of Charles IV, and the Mladota Palace (Faust House); other significant buildings include the Early Baroque Church of St Ignatius and the neo-Renaissance Czech Technical University building. The majority of the square consists of a park with seven sculptures and a Baroque fountain.
After the foundation of the New Town (Nové Město) by Charles IV (Karel IV) the place was called the Big Market (Latin: Forum Magnum), the New Town Square (Latin: Circus Novae Civitas) or the Upper Town Square. The importance of the square was supported by location of the New Town Hall (Novoměstská radnice) in its northern part. In the 15thcentury it was already known as the Cattle Market (Dobytčí trh). In the years between 1393 and 1791 in the centre of square used to stand the Divine Body Chapel with a small cemetery where Jan Kampanus Vodňanský was buried. It was abolished and demolished in 1784 under Joseph II. Before the construction of the chapel there was a tower where every second Friday after Easter imperial crown jewels and relics of saints were shown, which attracted many visitors from all the country and abroad. In the southern part of the square there was a prison hospital and thirteen old houses. According to the legend, by one of them there was a big marble stone with a carved cross, death’s head and year 1627. The stone is supposed to mark the place of executions where condemned spirituals and nobles were secretly executed at nights. Supposedly, the first execution in above mentioned year was carried out on several protestant priests who plotted a conspiracy against the emperor. In the northern part of the square stood a herring stall where dried fish, herrings and salt were sold. Before its demolition in 1862, it was known as Salle Romaine, which in French means the Roman room, and rented to various artistic groups, circuses and amateur companies.
Source: https://www.prague.eu/en/object/places/201/charles-square-karlovo-namesti