Purpose: Diagonal lashing is used to bind poles together that cross each other but do not touch when their ends are lashed in place in a structure.
Tying: Start with a single Timber Hitch around both poles. Wrap three or four turns around the two poles in one axis followed by three or four turns in the other axis. Tighten the lashing by surrounding it with three or four frapping turns. Finish with a Clove Hitch.
Animated Knots: http://www.animatedknots.com/lashdiagonal/