CHRISMON. – In diplomatics, this name designates the monogrammatic formula of invocation to the Divinity that document (v.). In the late Middle Ages it also came to be called labarum (cf. C. Du Cange, s. V. in Glossarium mediae et infimae latinitatis, V, new ed., Niort 1885, p. 2).
In its original form it is represented by the so-called Constantinian monogram (v. MONOGRAMMA COSTANTINIANO E MONOGRAMMA CRISTOLOGICO): and it is to this sign that the term c. properly applies. Over the course of the centuries, and from one country to another, it nevertheless underwent various transformations, often becoming complicated by ornamental signs that totally altered its appearance: so much so that in private documents of the 10th and 11th centuries it reveals the scribe’s complete ignorance not only of the origin but also of the meaning of the c. The most common forms range from the simple cross (sometimes also saltire, and, in the Greek or Latin form, now plain, now potent, now pommetty, now anchored), to a C (the initial of the Latin name Christus), generally intertwined with a long J (the initial of Jesus). Often the c. is added to the verbal invocation; at times it is accompanied by a pious formula, expressed in Tironian notes. In the papal chancery the monogrammatic invocation was used intermittently up to Leo IX; in the 11th century Gregory VII suppressed it definitively. The verbal invocation is found only once in papal documents (an act of Alexander II, dated 18 May 1972), for which one must think
The name c. is sometimes improperly applied also to the sign of the cross or a similar sign accompanying the subscriptions to the document: in this case it has simply the value of a religious symbol and generally denotes the personal intervention of the subscriber in the drafting of the document, both when there is an autograph signature and when it takes its place.