Christianity was introduced to Paris, formerly known as Lutetium, in the 3rd century. There were enough Christians in the year 250 for Pope Fabian to send the first bishop, Dyonisius, to Paris. He became Saint Denis, the patron saint of the city. At the time, Christians were persecuted. The bishop Denis had to practice the faith in secret, probably in a simple room in a house. Denis was killed a few years later with his helpers. His successors lived in hiding until the Emperor Constantine declared peace with the Church in 313. It was then possible to build Christian cathedrals.
Although several were known to be built in those early years, the Cathedral of Saint Stephen was the largest and most important. However, in the mid-12th century, under the reign of Louis VII, the current bishop made an extremely important decision: he decided to build a new cathedral. It would be much longer and taller than the previous one, since the new architectural techniques that were gaining favour, the ogival style, commonly known as the gothic style today, allowed it. That cathedral would become known as the Notre Dame Cathedral (1163-1182).