Four Corners of the Earth

There are several cultures in which, during ancient times, the earth was considered to be square (which, in today's article, is not the same as flat):

Hindu:

The basic plan of a Hindu temple is an expression of sacred geometry where the temple is visualized as a grand mandala. By sacred geometry we mean a science which has as its purpose the accurate laying out of the temple ground plan in relation to the cardinal directions and the heavens. Characteristically, a mandala is a sacred shape consisting of the intersection of a circle and a square.

The square shape is symbolic of earth, signifying the four directions which bind and define it. Indeed, in Hindu thought whatever concerns terrestrial life is governed by the number four (four castes; the four Vedas etc.). Similarly, the circle is logically the perfect metaphor for heaven since it is a perfect shape, without beginning or end, signifying timelessness and eternity, a characteristically divine attribute. Thus a mandala (and by extension the temple) is the meeting ground of heaven and earth. (An authentic Hindu mandala is traditionally a square within a circle.)

Daoism

In legend, the I Ching was developed from the He-Tu diagram. In the center, the five white/yang dots clustered together represents the rounded dome of heaven. The ten black/yin dots are arranged into a square that represents earth.

Ancient Egyptian

Some Egyptian depictions of the universe showed four pillars at each of the four corners of the world holding up the sky. The sky goddess Nut arched over her husband, the earth god Geb, also represents the curved or rounded heavens. She is sometimes held aloft by Shu, the personification of air.

I suspect the origin of the "square earth" or the "four corners of the earth" is, as many things are, astronomical in origin.

The Summer Solstice, coming up in just a few days, is instrumental in explaining this. The sunrise and sunset on the day before, the day of, and the day after the Summer solstice are at their northern-most latitudes. At the Winter Solstice, the opposite is true; the sunrise and sunset are at their southernmost latitudes for those of us living in the northern hemisphere.

To an observer whose eyes see for the same distance no matter what direction he looks in, the sunrise and sunset of the solstices describes a square. To ancient peoples, the rising and setting of the sun defined the edges of the earth itself. If the east-west edge was defined by the sunrise and set on the horizon, so, too were the north-south boundaries defined by how far north or south the sun rose and set.

The "four corners of the earth" then describe the points of sunrise and sunset at the summer and winter solstices!