It was foursquare; they made the breastplate double: a span was the length thereof, and a span the breadth thereof, being doubled.
A description of the high priest's breastplate.
King James Version (public domain)
Traditionally attributed to Moses · c. 13th century BC · The Pentateuch — Genesis, Exodus, Leviticus, Numbers, and Deuteronomy — is traditionally attributed to him
7And he put them on the shoulders of the ephod, that they should be stones for a memorial to the children of Israel; as the LORD commanded Moses.
8And he made the breastplate of cunning work, like the work of the ephod; of gold, blue, and purple, and scarlet, and fine twined linen.
9It was foursquare; they made the breastplate double: a span was the length thereof, and a span the breadth thereof, being doubled.
10And they set in it four rows of stones: the first row was a sardius, a topaz, and a carbuncle: this was the first row.
11And the second row, an emerald, a sapphire, and a diamond.