St. Longin's Rotunda is one of the few preserved romanesque rotundas in Prague, in the Czech Republic. It was founded in the 12th century as a parish church for a village called "Rybníček" which was there before the founding of the Prague New Town in the middle of the 14th century.
Originally, it was a Pagan temple before the arrival of Christianity, when it was transformed into a Catholic chapel.
Up until the 14th century, it was consecrated to St Stephen, before Charles IV founded the New Town and changed the consecration to Saint Longinus, who was one of the men who took part in Jesus' crucifixion, and supposedly pierced the side of Jesus.
Wikipedia https://en.wikipedia.org/wiki/St._Longin's_Rotunda
Official Website http://trojica.reckokat.cz/trojica/chram/rotunda
Address 12 Na Rybníčku, Praha 12000, Czech Republic
Coordinates 50°4'35.453" N 14°25'32.209" E