By Martin Bayfield
Former England and Lions second row
But where the role has developed since my playing days is that second rows have now developed into ball carriers.
They are - because of professionalism - fitter, stronger and more athletic, so they get their hands on the ball to take into contact.
They've also had to adapt a lot at the line-out because of the introduction of lifting. It's a bit more complex and the days of jumping in your one position are over.
There is a lot of movement and deception these days.
The second row that wears the number four shirt often jumps second in the line-out and is usually slightly shorter and is probably the bulkier of the pair.
Because the ball thrown to the two-jumper gets to him quicker, his is usually a more dynamic and powerful jumper, shooting forward.
He must be very quick off the mark and powerful. Martin Johnson was the master of this.
If you ever wanted to see a perfect example of a number two-jumper excelling, it would be during the Lions tour of Australia in 2001.
Justin Harrison famously pinched the line-out ball off Jonno during the third and final Test when the Lions were parked five metres from the Wallabies line.
There is also a difference at the scrum as well.
You either pack as the loose-head lock on the left side of the scrum, or you pack on the tight-head side, which is on the right.
The number four is more likely to be the tight-head lock.
Most of the pressure from the scrum comes through this side, you need your cornerstone on the tight-head side.
He locks out the scrum, he's the cornerstone and will usually be pretty stationary while applying a lot of the pressure.
"
The basic role of the second row remains the same - to lock and push in the scrum, win line-out ball and secure possession from restarts.
~RS~q~RS~~RS~z~RS~49~RS~)