String material and tuning

From the earliest of sources, the stringing of the cittern is described as a combination of "yellow" and "white" strings, presumably brass and iron, respectively. The "white" or iron strings were preserved for the top course and octave strings in the lower courses, with the "yellow" strings used from the 2nd course downward.

We are fortunate that the unique tuning common to all citterns of this time has a whole tone between the top two courses, as this is also where the transition from brass to iron stringing occurs. The move to iron was most likely necessitated by the need for a material that would not break at the desired pitch, which tells us with fair certainty that the breaking pitch of the brass was slightly above the tuning of the second course. This aligns well with our understanding of a top string pitch of e' being associated with instruments of a string length of approximately 43-45 cm. This knowledge can also be used to help us determine the proper tuning for citterns with shorter or longer scale lengths.

Octave stringing

Surviving evidence suggests that triple strung courses were strung with one fundamental string of twined brass and two octave strings of iron or steel, suggesting a preference for the higher partials that the octave strings provide. The general disposition of the fundamental strings, based on iconographical evidence, is that it is always was closest to the player--not placed in between the octave strings, as some online sources erroneously suggest. 

It is not clear if octave courses were used on double-strung instruments of more than 4 courses, for which two main tunings survive.  The woodcut from Kärgel and Lais’s Toppel Cythar (1575) depicts a fingerboard with five double-strung courses and a single top string, nominally tuned e'-d'-g-d-G-B (or b), in which the four lowest courses appear to pair a thick and thin string. This suggests that octave stringing was used, at least for this style/tuning of cittern, which was popular in Germany. (Four sources using this tuning survive.) On the other hand, Paolo Virchi's Il Primo Libro di Tabolatura di Citthara (1574), for 6-course cittern nominally tuned e'-d'-g-b-f-d-(G), is silent on the issue of octave stringing.  

String loops or no string loops?

Because of the way modern strings are made and packaged, many modern players expect that they need to use strings with individual loops. In practice, the stringing of the cittern does not require them, and surviving instruments with hitch pins have only as many hitch pins as courses (as opposed to on the English guittar, where one finds one hitch pin per string). All twined strings have one naturally occurring loop because of the way they are made. All of the plain strings, being two per course, can be made from a double length of wire that serves for both strings of the course. This can be accomplished by taking the string from one tuning peg, down around the hitch pin, and back up to the next peg. Complete instructions for this technique can be found in Publication 1: Stringing double-strung courses without using string loops.