Soldiers from four regiments and battalions have seen their old units merge to become the largest infantry unit in the British Army.
The Green Jackets served all over the world, including Iraq
The Royal Green Jackets took part in a cap-badge changing parade at Kiwi Barracks in Bulford, Wiltshire.
The parade marked the moment it became the 4th Battalion The Rifles.
Soldiers from three other regular units in England, Germany, Afghanistan and Iraq are holding similar ceremonies as they also become part of The Rifles.
The 1st Battalion The Devonshire and Dorset Regiment Light Infantry, the 1st Battalion The Royal Gloucestershire Berkshire and Wiltshire Regiment Light Infantry, and The Light Infantry will all reform.
The Rifles is now the largest regiment of infantry in the Army.
Lt Col Patrick Sanders, of the former Royal Green Jackets, described the merger as a "very happy marriage", which had not been forced.
"We all chose to come together," he said.
"These are four of the finest regiments in the Army and everybody wanted to take this step."
Each soldier in The Rifles now has the right to call himself a rifleman, an honour previously accorded only to the Royal Green Jackets.
They wear a cap with a badge featuring a silver bugle topped with a crown, evoking the history of the light infantry troops who first used the bugle, instead of the drum, to deliver messages across 18th Century battlefields.
Capt Baz Melia, of the former Royal Green Jackets, said the new regiment had a unique concept governing it.
"That is, that any soldier can decide to move to any location where The Rifles are stationed and he will fit in immediately.
The different battalions will be stationed in locations all over Britain including Chepstow, Exeter, Edinburgh, Yorkshire and Ballykinler in Northern Ireland.
The Rifles comprise five regular battalions, two Territorial Army (TA) battalions, and three TA companies in two separate TA battalions.
It will have many regimental associations and 12,000 cadets - a quarter of the Army Cadet Force.
The merger is part of the Future Infantry Structure, which was announced by then Defence Secretary Geoff Hoon, in December 2004.
It was decided the Arms Plot system - the mechanism by which battalions move and change roles every two to six years - was unsustainable.
Instead, individual battalions would be fixed by role and location.