As seen with The Immunes (or Specialized Class of Roman Soldiers), The Medicus was a Medical Professional which was used in a wide variety of Military operations. These were highly trained Specialists who most often began as Orderlies to Physicians in what would be considered Field Hospitals, today.
Physicians traveled with The Roman Legions on Campaign, to treat the wounded. From simple binding to amputations, as many as five such may have had to care for many hundreds, especially after a particularly brutal battle. Help was provided by The Orderlies. These Immunes were a type of Practical Nurse (of sorts), who provided basic care (dressing of wounds and physical assistance) to the wounded.
Some Medicus were trained to actually provide an early form of ''combat triage'' in the field. Some wounds were seen as making any trip back to a Camp to a Physician as fatal. Often, The Medicus (under fire in most cases), would assess the severity of the injury and stabilize the soldier for His trip back to a Physician. This this, The Medicus was the first true form of today's ''Combat Medic''.
It took many months to train a Medicus, and many years of experience – before a Medicus could actually perform as a Physician (in The Field). Often, especially in some of Rome's Campaigns in Germania and Gaul, The simple Medicus was the only Physician.
Officers (Noblemen), could afford to bring their own Physicians, often accompanying them into battle. If wounded, they stood a better chance at immediate treatment (whereas a Medicus was more concerned with the Common Legionnaire). When operating as the sole Medicus, of a Command, they were known as ''Medicus Duplicarius'' and paid double what a Medicus was paid (which was higher than a Legionnaire at any rate). They also held the ''Rank Authority'' of a Centurion.
Originally, Medicus were armed (Helmet, Armor and Sword), unlike The Legionnaire - The Medicus wore a White Tunic (Tunica) during The Republican Period. Later in Imperial Rome, the color Red was adopted (if for nothing more than to help cover the massive amounts of blood they often encountered).