Comment by thoughtpeddler

From my hazy recollection from law school, the US appeals courts are called "circuits" because back in the day, they weren't actual buildings but rather judges that would go around town-to-town within their jurisdiction in a horse-drawn carriage 'in a circuit' (that corresponded to a certain geographic area). The name just stuck even after they were permanently enshrined into physical structures (each corresponding to a given region).