The compass in a 13th-century manuscript is a symbol
of Creation; note the circular shape of the halo;
                          the word circle from the Greek
κίρκος/κύκλος (kirkos/kuklos),        itself a metathesis
of Homeric Greek κρίκος (krikos),
meaning "hoop" or "ring";  the words circus & circuit
closely related in origin:     the circle has been known
since before the beginning of recorded history;
natural circles would have been observed,
such as the Moon, Sun, &c., all of which form
circles w/in circles, all moving along circuitous paths;
the circle is the basis for the wheel, which,
with related inventions such as gears & pulleys,
makes much of modern machinery possible;
In mathematics, the study of the circle has helped
                     inspire the development of geometry,
                                              astronomy & calculus
                       [all of which was thoroughly known
                      well before known recorded history];

Early science,               particularly geometry
and astrology and astronomy, was connected
to the divine for most medieval scholars,
and many believed that there was something
intrinsically "divine" or "perfect" that
                    could be found in circles;
Some highlights in the circuitous history of the
concept of the circle are:
1700 BCE – The Rhind papyrus gives a method
to find the area of a circular field; the result corresponds to
256/81 [3.16049...] as an approximate value of π.
300 BCE – Book 3 of Euclid's Elements
deals with the properties of circles;
In Plato's Seventh Letter there is a detailed definition
& explanation of the circle; Plato explains the perfect circle,
and how it is different from any drawing,
words, definition or explanation;
1880 CE – Lindemann proves that π is transcendental,
effectively settling the millennia-old problem
of squaring the circle
Although usually associated with women
of high-ranking noble families tiaras & have been worn
by commoners as well, especially rich American
                              socialites like Barbara Hutton;
Tiaras are generally semi-circular      or a circular band,
usually of precious metal, decorated
with jewels & worn as a form of adornment;
On rare occasions, usually when the actual tiara
is exceptionally old, or contains valuable gemstones,
realistic copies may be made & worn in place of the original
due to insurance considerations;   Tiaras are worn by women
around their head or on the forehead as a circlet
on very formal or high social occasions.
                   Tiaras are used in the crowning of beauty queens