St. Stephen's Cathedral is the main church of the Archdiocese of Vienna and the seat of its archbishop. It was begun by Rudolf IV of Austria and stands on the ruins of two earlier churches, the first of which was a parish church consecrated in 1147. The building has also undergone several alterations and extensions throughout its history, following different artistic styles. It is the most important religious symbol of Vienna and has witnessed many events in Austrian history.

On the outside of the building you can see the roof, the two bell towers - the south and north towers - and the entrance porticoes to the church: the Singers', the Towers', the Bishop's and the Giant's. The Pummerin bell is the most important bell tower in the church. The Pummerín bell is a reconstructed version of the original bell, which was damaged by fire.

The interior of the cathedral consists of three naves and numerous altars, each of which houses a variety of objects and works of art that were donated by different personalities. As in all temples, burials used to take place under its floors, which is why the place preserves the tombs of several of the country's nobles.

In the mid-12th century, Vienna had become an important centre of [French-German] civilisation in Eastern Europe, and the four existing churches, including only one parish church, were insufficient to meet the religious demand.

In 1137, the bishop of Passau, Reginmar, and Margrave Leopold IV signed the Treaty of Mautern, where Vienna is referred to as "Civitas" for the first time, and St. Peter's Church is transferred to the diocese of Passau. According to the treaty, the bishop donated the land beyond the city walls to Margrave Leopold IV, with the notable exception of the territory allocated to the new parish church, which was to become St. Stephen's Cathedral.

Although previously believed to have been built in an open field outside the city walls, the new parish church was probably built in an ancient cemetery dating back to Roman antiquity; excavations in 2000 to install a heating system uncovered tombs 2.5 metres below the surface, which were dated to the 4th century using the carbon-14 technique. This discovery suggests the existence of a religious building even earlier than the Ruprechtskirche.

The history of the church begins in 1137 with a Romanesque church, which was rebuilt in the late Romanesque style some 100 years later. In the 17th century it was extended in the Baroque style. The Romanesque portico is flanked by the two Towers of the Pagans, both 64 metres high. The unfinished north tower, with a height of 68 metres, was closed in 1579 with a Renaissance roof. During the Counter-Reformation period, the cathedral was fitted with Baroque decorations. Some of the elements have an associated symbolism: the gargoyles on the outside represent evil spirits.

This parish was consecrated to the patron saint of Passau Cathedral, St. Stephen. In 1137, all other churches in the city were placed under the jurisdiction of this parish church.

In April 1147, the partial consecration of the church, which was still under construction, took place in the presence of the bishop of Passau. Its dimensions were exaggerated for Vienna at the time, indicating the foresight of its creator, who was preparing it to become a bishop's see or duchy church.

This parish church was completed in 1160 and, at 83 metres long, had the profile of a cathedral. It was oriented in the same way as the present church, towards the point of sunrise on 26 December 1137. Almost nothing remains of the old church, although archaeological studies have revealed the dimensions of the central nave, which was 12 metres wide (about 26 metres if the three naves are added together) and 83 metres long, including the apse.

The second Romanesque building, begun in 1240 and consecrated in 1263, of which the western façade with the gigantic doorway remains, was essentially promoted by the new powers, the bourgeoisie and the ducal house.

The construction of the new Gothic building of St. Stephen's began in 1304. The spacious nave, one of the widest in Europe, testifies to the fact that the bourgeoisie was able to achieve a dominant position here. The choir was built between 1304 and 1344. From 1359, the side walls of the central nave began to be built, enclosing the old Romanesque nave like a sheath. It was not until 1446 that the last vaults under the gigantic roof were completed. Between 1359 and 1443 the southern tower was erected. The first lightning bolt that strikes the high altar and illuminates the place is used as a symbol of the open sky which, according to the Acts of the Apostles, St. Stephen was able to see before he died.

The only surviving parts of the old building are the Black Chamber, which is located on a lower level of the south Pagan Tower and now houses a confessional, and part of the ground floor on the west floor.

In terms of their symbolism, the gargoyles placed on the outside of the temple had the function of frightening away evil spirits: for the same purpose, material from Rome was used in the construction of the temple, as it was believed that sanctified pagan stones took away their power.

In the right inner arch of the Giant Portal there is a Roman tombstone that is barely legible. In 1996, the figure of a hidden woman, the Mirona, was identified as coming from another Roman tombstone. In the Portal del Obispo, in a latticed niche, were the so-called Tartars; pagan divinities: a legend that can still be seen warns about the veneration of these idols, and invites us to respect the Christian faith. Under the clocks of the Pagan Towers there are representations of a phallus on the left and a vulva on the right: they represent a pagan sanctuary dedicated to a fertility divinity. Recent excavations at the Giant Portal have uncovered a large number of graves.

There is also a numerical symbolism: the windows of the side aisles, the place for the faithful, are made up of four parts; those corresponding to the choir, where the Eucharistic mystery takes place, are made up of three parts. The top of the tower with twelve pinnacles refers to the twelve Apostles gathered around Christ. The pulpit railing is composed of three and four lobes forming a wheel.

The cathedral also has some arithmetical relationships: it is 111 feet (35.52 metres) wide, and its length is three times 111 feet. The height of the south tower is 444 feet, four times 111 (136.08 metres), and there are 343 steps (73) to the south tower chamber.

Today the measurements have changed slightly: the temple measures 107.2 metres in exterior length, and the total width of the three chancels is 34.2 metres. The central nave is 28 metres wide, and the side aisles are 22.4 metres wide.