The Plan depicts an entire Benedictine monastic compound including churches, houses, stables, kitchens, workshops, brewery, infirmary, and even a special house for bloodletting. The Plan was never actually built, and was so named because it was kept at the famous medieval monastery library of the Abbey of St. Gall, where it remains to this day. It was drawn in a scriptorium in Reichenau in the third decade of the 9th century, dedicated to Abbot Gozbert (816-836) of Saint Gall.
The Plan was created from five parchments sewn together measuring 45 inches by 31 inches (113 cm by 78 cm) and drawn in red ink lines for the buildings, and brown ink for lettered inscriptions. It is drawn to an "unusual" scale of 1:192 (although as explained in detail in the "The Plan of St. Gall in brief" by Lorna Price, this is 1/16" to the foot, which would not be so surprising as necessary to place the overall plan onto this size piece of parchment). The reverse of the Plan was inscribed in the 12th century, after it had been folded into book form, with the Life of Saint Martin by Sulpicius Severus. About 350 partly rhyming appendices in the handwritings of two different scribes describe the functions of the buildings. The dedication to Abbot Gozbert is written in the margin.
Because the plan does not correspond to any place that was actually built, just about every aspect of the Plan is disputed by modern scholars. Debates continue on things such as which system of measurement was used; whether the scale is a single scale for the entire plan or varied for different elements; if the plan is a copy from a lost prototype or the original; if it is reflective of a single individual's ideas, or those of monastic council.
Despite the unknowns, much has been learned about medieval life from the Plan. The absence of heating in the dining hall, for instance, may not have been an oversight but was meant to discourage excessive enjoyment of meals. In the quarters for the 120-150 monks, their guests, and visitors, the ratio of toilet seats was better than what modern hygienic codes would prescribe.
For thee, my sweetest son Gozbertus, have I drawn this briefly annotated copy of the layout of the monastic buildings, with which you may exercise your ingenuity and recognize my devotion, whereby I trust you do not find me slow to satisfy your wishes. Do not imagine that I have undertaken this task supposing you to stand in need of our instruction, but rather believe that out of love of God and in the friendly zeal of brotherhood I have depicted this for you alone to scrutinise. Farewell in Christ, always mindful of us, Amen.The Latin reads:
Haec tibi dulcissime fili cozb(er)te de posicione officinarum paucis examplata direxi, quibus sollertiam exerceas tuam, meamq(ue) devotione(m) utcumq(ue) cognoscas, qua tuae bonae voluntari satisfacere me segnem non inveniri confido. Ne suspiceris autem me haic ideo elaborasse, quod vos putemus n(ost)ris indigere magisteriis, sed potius ob amore(m) dei tibi soli p(er) scrutinanda pinxisse amicabili fr(ater)nitatis intuitu crede. Vale in Chr(ist)o semp(er) memor n(ost)ri ame(n).
According to Horn, the Plan was a copy of an original blueprint of an ideal monastery created at two Carolingian reform synods held at Aachen in 816 and 817. The purpose of the synods was to establish Benedictine monasteries throughout the Carolingian Empire as a bulwark against encroaching Christian monastic missionaries from Britain and Ireland who were bringing Celtic lifestyle influences to the Continent (see Celtic art).