An interweaving cross in heraldry is known as a Fretty Cross (Fr. Frettée). With a somewhat tighter weave it would be called a Trellised Cross.
The cross is not restricted to heraldry, of course, and below we look at the design in a Christian context.
'Fret' has several meanings, all of which originate from the Old English freten: to eat up, to consume. To fret about something is to worry or be annoyed about something that has eaten away our patience or contentment.
When ocean waves crash against the cliffs, this fretting is more commonly known as 'erosion'. The fretting of gently flowing rivers or slow moving glaciers carves out new channels through the rocks. Similarly, wind and rain eventually fret even the hardest rock. (Hard rock? Yes, I'll tell you something about rock'n'roll shortly.)
In manmade fretwork, material such as wood or metal is cut away to form intricate patterns, some of which may give the appearance of overlapping or interlaced bands, as we see in the Frettée Cross.
Fret in centre of Koceljeva Flag
This symmetrical design is simple to copy and consequently a popular decorative pattern, especially in heraldry. It appears, for example, in the coat of arms of the Harrington family of Suffolk and Essex, leading to an alternative name: the Harrington Knot. It's a main feature also in the flag of Koceljeva, in Serbia.
The overlapping nature of the pattern means that some lines are, or appear to be, raised (relief), and this is why the raised ridges set across the fingerboard of a guitar are called frets. Guitar frets can wear out after many years' use, especially when techniques such as right-hand fretting are used in heavy-metal rock. But replacement frets are cheap enough so there's no need to fret about fretting frets.
Just as a twisted rope is stronger than straight individual strands, interweaving material adds strength. Paradoxically, a structure which is designed around depletion (fretted), leads to something stronger.
This anomoly can also be found in the Bible: When Jesus was crucified on the cross, the persecutors' intention was to destroy an unwanted prophet. But instead, the Crucifixion had the opposite effect. See the Meaning of the Cross.
The photo on the right, kindly sent to us by May Brit Lysa in Denmark, shows a silver pendant with twelve interweaving bars.
This not only reminds us of Christ's command to his twelve disciples to spread the Gospel, but also the hipostatis that God is three Divine Persons bound together as One, and that we can also be bound in the love of God.