The inner, oldest Mühlhausen city wall was almost 2.8 kilometers long (2.2 kilometers of which have been preserved to this day) and enclosed an area of around 50 hectares. This area had the shape of a somewhat rounded and not quite even rectangle, whose maximum east-west extension is almost twice as long (1000 meters) as its maximum north-south extension (500 meters). Its original layout included the four main gates, namely the Görmartor in the north-east, the Erfurter Tor in the south-east, the Felchtaer Tor in the south-west and the Frauentor in the north-west, named after the Marienkirche (= Church of Our Lady), as well as probably four gates: the Eselspforte and the Burgpforte on the north side as well as the - unknown by name - gate at the exit of Brunnenkreßstraße and a further, only accessible gate to Spielbergstraße on the south side.

Whether the original main access to the castle via Breitenstraße was closed when the wall between the castle and the town was built before 1251 or only after the castle was demolished from 1256 is unclear.

The material used for the inner (and later also the outer) town wall, including the gates and towers, was travertine, a geologically young freshwater limestone found in Mühlhausen and quarried here.

The inner city wall was built as double-shell masonry. Its thickness up to the height of the battlements varies between around 1.5 meters and - only exceptionally reached - a maximum of 2 meters.