The letter S is a graphic stunt. Having grown out of the w/tooth-looking Proto-Sinaitic Shin letter, it stood up on its Greek-Σ feet – littera erecta – before shedding its angles for more alluring curves.
Both the letter S and its ancestor sigma Σ are drawn in zigzag, right to left, left to right, and so on until the sign is complete. This kind of zigzagging was a common way of writing in stone in Ancient Greece and is called boustrophedon. The word means ‘in the manner of oxen’, because ploughing with oxen is bi-directional, in a zigzag across the field.
The manner of drawing the letter S may hark back to bi-directional writing, before it was replaced by left-to-right or right-to-left script systems, like Greek/Latin or Hebrew/Arabic, respectively. The letter S is bipartisan, finding common ground while ploughing the entire writing field in sweeping motions.
It is a stunt – an act of graphobatics, we might say. Like several other letters, it doesn’t need pen lift – staying close to the ground. Unlike any other letter in the alphabet, it is graphically recursive without any pen lift: it can be repeated vertically without lifting the pen off the page, like an unending zigzag going down.
Nowhere is the letter’s stunt-potential more clearly emphasized than in a decorated initial from a 12th-century manuscript, displayed above. The anthropomorphic design shows 4 jugglers testing the limits of the letter with dangerous activities: one is juggling with knives while two appear to pass a sword between themselves.