"They’re called crinkle crankles. A single leaf wall over that distance would need brick piers approx every 1.5-2m if it was a retaining wall it would need to be at least 9” wide (2 bricks). The crinkle crankle has more strength due to it’s curved nature so can be 4” wide or a single leaf of bricks.
For the maths if we can assume they’re true semi-circles then each semi circle would be 1/2piD or 1.57D whereas a double leaf wall would be 2D for the same length D
Therefore using 21.5% less bricks than a double leaf wall"
#20 Legibly. Or it would be completely black.