The ancient Greek Kithara & Lyra generally had 7 strings - for the ancient Greeks, music represented the harmony of the Universe & so for them, the number 7 was spiritually significant - it could represent for them, the Seven Celestial Spheres...
According to the research of the musicologist Curt Sachs in his book "The Rise of Music in the Ancient World - East and West" (page 230), the following tunings for the standard 7 string ancient Greek lyres can be inferred for the following surviving pieces of written music from ancient Greece (the tunings are all descending - in the tuning below, the first E is at the top string and the D is the bottom string):
ED BAG ED
2nd Hymn to Apollo
EDC AG ED
Hymn to the Muse
Hymn to the Sun
Hymn to Nemesis
Bellerman's instrumental piece
Another possibility, taking into account E being sharpened to F and then adding that 7th string below:
F DC AGFE
1st Hymn to Apollo
All these would be "open-string" tunings as inferred by the preserved melodies Sachs discusses.
For me, however, one of the greatest mysteries, is how did the ancient Greeks managed to play some of the often complex & chromatic music of ancient Greece (as testified by the 60 or so fragments of ancient Greek music so far discovered) on a diatonically strung lyre with just 7 strings? In the famous 'Skolion of Seikilos', for example, the notated melody has a C (4th degree of the mode starting on G - the only way to play this on a 7 string lyre is to use the knuckle or nail of the left hand thumb as a fret on the string to raise its pitch by the required semitone - a technique also inferred by Sachs.
If this hypothetical 'string stopping' technique was not used, then one must conclude that the lyre simply 'filled in' some sort of either arpeggio-style or morerhythmic 'block and strum' style of accompaniments to the vocal line, rather than exactly mirroring it, similar to the block and strum still practiced today by African lyre performers...what a pity the ancient Greeks did not leave any MP3s of their music to rest the case either way!
So, below is a video of one of my live "archaemusicological experiments", in which I attempted to play an actual fragment of ancient Greek music (The First Delphic Hymn To Apollo, c.128 BCE) on just 7 strings, in an attempt to further verify the theory expounded by Curt Sachs that the ancient Greeks must have used some form of "finger stopping" (using either a knuckle or finger of the left hand as a fret on the lyre string) in order to play the accidentals clearly indicated in some of the extant surviving fragments of ancient Greek music:
There are, of course, arguments against the hypothesis of this technique of finger stopping to create accidentals on a lyre - there is no evidence of using it among cultures perceived to be ancient Greek music successors. For example, in Africa, where all manners of lyres have been played continuously since antiquity, this technique is never seen.
However, the fact remains, that the ancient Greeks clearly indicated the use of chromaticism in so much of the surviving music that has been discovered - string-stopping on the lyre is the only way available, to produce these accidentals - and as can be seen in my experiment, the method proposed by Sachs works perfectly on the sort of low tension natural fibre or gut strings which would have been used on the Kitharas & Lyras once played in ancient Greece...
EVIDENCE OF THE STRING-STOPPING TECHNIQUE IN ANCIENT EGYPT?
For me, the most compelling evidence for Curt Sach's hypothesis on the use of string-stopping on the ancient Greek lyre to produce chromaticism, is the even earlier evidence of the same technique in use, at least a thousand of years before the Golden Age of ancient Greece, as practiced by the harpists of ancient Egypt.
There is a fascinating PDF article abut the ancient Egyptian harp from a book excerpt "Ancient Egyptian Musical Instruments" by Moustafa Gadalla, which I recently discovered, featuring an illustration of a relief from tomb 11 in the Ta-Apet (Thebes) area (New Kingdom 1520 BCE): a harper shortens the string with one hand,and plucks with the other - this is surely the first unambiguous pictorial evidence of the technique of string-stopping from the ancient world! The bent string is clearly shown:
Also, the book excerpt mentions that "in Idut’s Tomb [c. 2320 BCE], two of the five depicted harpers pluck with only the right hand, while the left one holds down the string"
If string-stopping was an established ancient Egyptian harp-playing technique for playing chromatics, in use from at least as early as 2320 BCE, then surely there can be no problem with Curt Sach's hypothesis that it was also being used 2000 years later, by the lyra & kithara players of Classical Greece?
For me, this illustration from ancient Egypt, is the "smoking gun" to prove the existence of Curt Sach's hypothesis of the finger-stopping technique to play accidentals on a diatonically strung lyre or harp - & even more significantly, the existence of this finger-stopping technique is evidence of an understanding of chromaticism by the musicians & composers of antiquity, dating back over 4000 years!
The music of the ancients must have been more complex, developed & refined than we could ever have previously imagined...