In the Sumerian lexical lists, PIR is broken down as PI with ER. PI is knowledge, a symbol of sacred geometry. This refers to the (musical) pitch, to the perfection of it, to the first syllable of words such as perimeter (PI-RE) and perception. ER is source of ‘err’, meaning to wander and is given as ‘to go’. Plato called his character Er for that reason.
UD/PIR, pyramids of the sun, of the day, of time and, of course, the measurement of everything.