Squaring the Circle – G K Chesterton on Circles and Crosses:
As we have taken the circle as the symbol of reason and madness, we may very well take the cross as the symbol at once of mystery and of health. Buddhism is centripetal, but Christianity is centrifugal: it breaks out. For the circle is perfect and infinite in its nature; but it is fixed for ever in its size; it can never be larger or smaller. But the cross, though it has at its heart a collision and a contradiction, can extend its four arms for ever without altering its shape. Because it has a paradox in its centre it can grow without changing. The circle returns upon itself and is bound. The cross opens its arms to the four winds; it is a signpost for free travelers.
(from Orthodoxy chapter 2)