The main sewage drain ran along the western front of the legionary camp, immediately adjacent to the camp wall. It lay under the road parallel to the camp wall (via sagularis) and formed part of an extensive subterranean sewage system. The system as a whole is estimated to have been more than five kilometres long, running through the entire camp.
Built out of stone, the drains were used for the latrines, thermal baths and well overflows, also ensuring fast drainage of water from the roofs and roads when it rained. The large sewage drain collected the effluent from the smaller side drains, allowing it to flow directly out of the camp to the River Aare in the north.
A functional drainage system was required so as to prevent the spread of disease and epidemics in the legionary camp. Together with the troop toilets, thermal baths and camp infirmary, the drainage system was one of the most important hygienic facilities in keeping the approx. 6,000 legionaries healthy and therefore fit for action.
The sewage drain was discovered as long ago as 1899. It was investigated once again in 1907 and the excavator at the time named it the "Cloaca Maxima of Vindonissa" - in reference to the monumental drainage system in Rome itself. In order to make the sewage drain accessible to the public in the early 20th century, a section measuring at least 20 metres in length was preserved. After this the "Cloaca Maxima" was neglected. It was not until some 100 years later that it was possible to open up the drain to Legionary Path visitors: measuring two metres in height and one metre in width, it can be conveniently accessed.
The main sewage drain can be visited with museum admission.