The Lions head coach believes that the scrum will be a key battleground for next year's tour; and so the appointment of Rowntree, the former Leicester Tigers, England and Lions prop is the final piece in the coaching jigsaw for McGeechan. He'll be working alongside assistant coaches Warren Gatland (forwards), Shaun Edwards (defence) and Rob Howley (backs).
Davies said of the appointment, "Graham is an unremitting professional who'll bring much to our play against the South Africans. A rugged scrummager in his playing days but with a growing reputation now as a specialist coach he is an important addition to the coaching team."
McGeechan added, "I am delighted to have Graham on board. He brings with him a direct approach and an understanding of not only what we are looking to achieve as a coaching group but also an understanding of the Lions ethos.
"The scrum will be an intensely contested area in South Africa and we'll need to be technically accurate at scrum time from the moment we arrive. It is crucial to have a forward pack that are technically as good as they can be against a renowned set of South African forwards."
Rowntree joined the Lions pair at Heathrow and talked of how eager he was to make this a historic tour.
"It is a tremendous honour to be asked to become involved with Geech's coaching set up.
"Having experienced both the highs and lows of Lions rugby as a player, I am determined to be part of a winning set up in 2009 and am relishing the opportunity to work with the other coaches to make that happen.
"Geech is someone that I have an enormous amount of respect for and I cannot wait to play my part in contributing to a great rugby environment."