Page 22 - Berndt Sundsten "My First Book of Knots: A Beginner's Picture Guide"

The square knot

(reef knot) is a classic knot. It has been used by sailors throughout history to
hold bundles and packages together. The square knot is probably the most
common and well-known knot. Tie it so that the rope ends exit each bight
where they entered it, and the two ends come out on the same side of the
knot.

According to one story, sailors made a thief knot (a variation of the square
knot in which the ends come out on different sides of the knot) around their
sailor’s sacks. Anyone opening the sack would, out of habit, make a square
knot to close it again. This was how a sailor could see if someone had been
looking in his sack.

A much better (sturdier) knot than the square knot is the sheet bend, which is
one of the oldest known knots. It is particularly good if you want to join two
lines with different diameters. You’ll find it on page 16.