Built by children near the shore Protected by knights in historical lore

Despots fear me ‘Rebels’ seek me Every human yearns for me But sadly, some places I cannot be.

Many legends give me different appearances but I am also real. In the past I have a crown and scales of a different color than I do now. In real life, watch me run. Otherwise avert your eyes and hold your breath.

Low-level labyrinth, mortuary maze, Or a means to pick nits, from flea-ridden strays?

A crest in the west, a patron in east. Big and powerful in the west, old and wise in the east. From mythos I am, not real but a tale. What am I?