The oldest church building (of which nothing remains today) dates back to the Early Middle Ages, and there is speculation that it could be the oldest church in Vienna (See Ruprechtskirche). The church is believed to have been established by Charlemagne around 800, although there is no evidence supporting this view. In any case a church of Saint Peter in Vienna is first mentioned in 1137. Around the end of the 12th century, the church became part of the Schottenstift.
The mediæval church had three altars, with an apse in the south instead of the normal eastern orientation. This unusual feature has triggered many discussions among experts, and it is suspected that the church was adapted from a previously secular building. The church was surrounded by shops and a nearby building housed the Stadtguardia, a forerunner of the modern police. The old church burned down in 1661 and was given only makeshift repairs. The decision to build a new church was taken up in 1676, with the arrival of the Trinitarian Order. The construction of a the new church was begun around 1701 under Gabriele Montani, who was replaced by Johann Lukas von Hildebrandt in 1703. By 1722, most of the building was finished. The new church was the first domed structure in baroque Vienna. It is built in a very compact form, with its oval interior housing an astonishing amount of space and rectangular attachments.

The dome was mainly designed by Matthias Steinl, and the frescoes by Andrea Pozzo, whose paintings were removed after his death. As a result, in 1713, Johann Michael Rottmayr was able to start a completely new set. The high altar was created by Antionio Galli-Bibiena (construction) and Martino Altomonte (altarpiece). Over the years, the paintings have become darker, and the interior began to take on a grey appearance. From 1998 to 2004, the church underwent a renovation, which returned the paintings to their original rich colouring and brightness.
The Peterskirche is located on Petersplatz, right next to Graben and just west of the Pestsäule. The street Jungferngasse cuts through the pedestrian zone and leads directly to the church. The Peterskirche is largely obscured by the surrounding buildings, and can only been seen clearly from directly in front.

Text Source: Wikipedia