The Crown Legion is the personal legion of the First Lord. It serves only him, and is composed of troops from the area around Alera Imperia.
The original Crown Legion was under the command Gaius Septimus when it was deployed in the Calderon Valley during the Battle of First Calderon. The Legion was destroyed to a man by a surprise attack from a Marat horde.
The Crown Legion was recreated in Academ's Fury by the First Lord Gaius Sextus command. The Legions Captain position was given to Sir Miles. Some viewed this as move by Sextus negatively as some seen this as an act of growing insanity or insecurity.
During Cursor's Fury, the Legion was camped in the Amaranth Vale near Ceres when the forces of High Lord Kalare attacked the city. Gaius Sextus gave the command for the Crown Legion to force march to aid Ceres and get within the city before Kalare's legions reached it. The Crown Legion fought alongside Ceres's remaining Legion/s and defended the city long enough for a small rescue team to rescue the High Born hostages from the city of Kalare.
In Captain's Fury the prologue shows the Crown Legion and the Legions of Aquitainus Attis fighting against Kalere's forces in the Southern Theater of the Kalare region. The Crown Legion forces has sustained heavy casualties, as well as debilitating sickness, with a ratio of 1 man dying in battle to 3 dying because of sickness. Aquitainus Attis was also subtly manipulating his Legions so that the Crown Legion takes more damage during battle.