Each standard, or signum, was unique to its "Century" and was composed of a number of philarae (disks) together with a number of other items such as circles and crescents to representing astrological elements.

Purpose of the Roman Standard
Each Roman centurion led 100 Roman Soldiers. Junior officers reporting directly to the centurion included the standard bearer and signifier for each century. The Roman ensigns and standards standards helped to keep the units together, since the soldiers could see them above the action. There were a large number of standards and ensigns in the Roman Army making them readily visible to the soldiers. The purpose of the Roman standards were to act as follows:

• Recognition signals for the various units in battle
• Rallying points
• Used in combination with the horn blowers and trumpeters to signal the troops
• Symbols of Roman power and honor
• Key symbols of the Roman army and soldiers in religious ceremonies
• The various standards were considered as sacred objects representing the spirit and soul of the various military units

Different Types of Roman Standard
The different types of standard, or signa militaria, were:

• The Standards (signa or signum)
• The Banners, rectangular flags of different sizes used for a variety of purposes. A large red banner was the special ensign of the general
• The Manus was the open hand at the top of the maniple standard
• The Vexillum (vexilla) was a small rectangular flag attached vertically to a cross-bar carried on a pole
• The Aquila was the eagle standard which was the supreme symbol because of its association with the god Jupiter
• The Draco was the cavalry standard of each cohort flown like a modern wind sock
• The Imago which represented a likeness of the Emperor and sometimes depicted astrological signs

History of the Roman Standard
The signa militaria were the Roman military ensigns or standards (flags) the origins of which dated back to the very beginning of Rome. The most ancient standard used by the Romans was a handful (maniple) of straw of fern fixed to the top of a spear. Therefore the company of soldiers belonging to it was called a Maniple (Manipulus). This primitive standard was replaced by the figures of real and mythical animals which according to Pliny the Elder were the eagle, the wolf, the minotaur, the horse and the boar.

History of the Roman Standard - The Meaning of SPQR
The letters SPQR were often seen on the Roman standard. The standard displaying SPQR stood for the Latin words 'Senatus populusque romanus' meaning the 'Senate and people of Rome'. 

History of the Roman Standard - The Aquila
During the reorganisation of the Roman army by the general and consul Gaius Marius (157 BC–January 13, 86 BC)  only the eagle (Aquila) was retained. The eagle standard (Aquila) was made of silver, bronze or even gold displaying with outstretched wings. It was considered the greatest disgrace and a portent of bad luck to allow the eagle standard to fall into the hands of the enemy. The Aquila was therefore designed small enough to be concealed on the person of the standard bearer.

History of the Roman Standard - The Vexillum
Each cohort had for its own vertical standard or flag (Vexillum or vexilla) which was woven on a flag - a square piece of cloth (textilis anguis) with tassels and elevated on a gilt staff. The vexillum banner generally designated the Unit Type of "LEG" (Legion) or "COH" (Cohort) and the Unit Number in Roman Numerals.

History of the Roman Standard - The Manus
The Manus was the open hand at the top of the maniple standard signifying the oath of loyalty taken by the soldiers. The manus would sometimes have a laurel wreath added if the maniple troop had been recognised for this honor.

History of the Roman Standard - The Imago
The Imago which represented a three-dimensional gilt likeness of the Emperor as a constant reminder of the troop's loyalty to him. An imago standard might also depict astrological signs representing the period of the Zodiac under which the legion or unit had been formed.

History of the Roman Standard - The Draco
The Draco was the cavalry standard of each cohort flown like a modern wind sock. This standard consisted of the bronze head of an open-mouthed dragon with a long fabric body attached which resembled the long body or tail of a snake or a serpent. The standard was elevated on a gilt staff and carried by a cavalry signifer called a draconarius. As the draconarius galloped along the ranks wind flowed through the open-mouthed dragon and billowed out the cloth tail much like a modern wind-sock. There is some speculation that a loud whistle was added to the Draco to unnerve the enemy. 

Roman Standard Bearers
Signifer was the general name given to all standard bearers. The names of specific Roman Standard bearers were as follows:

• Aquilifer: The Aquilifer was a Senior Officer who carried the eagle standard (Aquila) of the Legion. This prestigious role was extremely important and prestigious position

• Signifer: The Signifier was a Senior Officer who carried the Century's standard (signum) into battle and was also the treasurer for the Century

• Draconarius was a Roman cavalry standard bearer

• Imaginifer: Carried the three-dimensional gilt Imago Standard bearing the image of the Emperor

The Roman Trumpeters and Horn Blowers
The Roman trumpeters and horn blowers worked closely with the standard bearers, and were used in combination to signal the troops. Orders to retreat, advance could be heard above the battle noise. At the soldiers camp orders such as 'assemble' or 'leave camp'  or 'change watch' were conveyed by the shell horn instruments. The musical instruments used by the Roman Army and the names of the musicians were as follows:

• The trumpet (tuba) - the Trumpet players were called the tubicines

• The lituus - a variant of the tuba with a curve at the end played by liticines

• The horn (cornu) - he horn-blowers were called the cornicines

• The shell-horn (bucina) - the horn-blowers were called the bucinatores

The Roman Trumpet
The Roman trumpet called the tuba, played by the tubicines, was about 3 feet long with a funnel-shaped opening. The lituus was a variant of the tuba with a curve at the end played by liticines

The Roman Horn
The Roman horn, called the cornu and the shell horn the bucina, were played by the cornicines. The cornu was a large curved instrument and the bucina resembled large shells.