What did a medieval stonemason do when heavy rainfall interrupted his work? Umbrellas are impractical at construction sites. Gore-Tex jackets weren't yet invented, nor were plastic rain jackets. "He donned a jacket made of felted loden cloth," says Bert Geurten, the man who plans to build an authentic monastery town the old-fashioned way.

Felted loden jackets will also be present on rainy days at Geurten's building site, which is located near Messkirch, in the southwestern German state of Baden-Württemberg, between the Danube River and Lake Constance. Beginning in 2013, a Carolingian monastery town will be built here using only the materials and techniques of the 9th century. From the mortar to the walls, the rain jackets to the menu, every aspect of the operation will be carried out as just as it was in the days of Charlemagne. "We want to work as authentically as possible," says Geurten.

The building contractor from the Rhineland region has long dreamt of carrying out his plan. When he was a teenager, the now 62-year-old was inspired by a model of the St. Gallen monastery plan in an exhibition in his home city of Aachen. The plan, dating from the beginning of the 9th century, shows the ideal monastery, as envisioned by Abbot Haito of Reichenau....