Geisa is mentioned first in a written document in 817 AD as a property of the Benedictine abbey of Fulda. Its oldest area of settlement is located on "Gangolfiberg", which is the highest point of the town proper (at 322 m NN). This is also the location of the only surviving medieval place of jurisdiction in Thuringia, the so-called "Zentgericht" - dating from around the 11th century. A town wall, still largely extant today, was built around the year 1265. The deed of town ordinances and privileges was lost, the first notation as "civitas" is from 1302.