The Roman Empire managed to conquer most of Europe and stay united for centuries. Knowing this, it’s surprising not to find a symbol that represented the entirety of the Empire. Did the Romans rely on flags to feel they were part of the same territory?
The Roman Empire didn’t have a flag as people know them today. Rome was a collection of territories with different cultures and symbols. However, standards were used to identify Roman legions, and SPQR came to symbolize the Roman Senate and its citizens.
What joined the Roman Empire together wasn’t a flag but a vast network of infrastructure and bureaucracy. Still, some symbols managed to prevail, especially in the military.
Also see Did the Romans Like Julius Caesar? to learn more.
What Were the Roman Empire Standards?
Roman standards were banners or figures attached to poles that identified a legion or a smaller group of soldiers. Their function was to give courage to the soldiers and serve as a point of reference for giving orders.
Roman standards were a crucial part of the functioning of a Roman legion, both during battles and outside of them.
When Roman legions decided on a place to camp, the first thing they did was press their standard into the soil. Standards carried a quasi-religious significance, and this act was believed to carry omens. 
During battle, the eagle standard of a legion and the personalized standards for each century gave the legionaries courage. However, they also had a practical purpose.
Standards were so present in the minds of Roman soldiers that they were used as points of reference for strategizing and doing operations in the heat of battle.
For example, signa inferre was an order to advance, and signa referre an order to retreat. The word “signa” referred to the standards. Because they were placed high up in poles, standards acted as reference points for soldiers, allowing them to locate themselves and identify their allies.
When a century became dispersed in the middle of a fight, standard carriers would call using his voice or a horn to regroup around the banner.
Carrying a standard was a high honor, and soldiers protected them with their life. It was crucial to hide standards from the enemy. A harmed standard carrier would do his best to deliver it to his general before dying and leaving the banner on the battlefield.
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What Did SPQR Mean in Ancient Rome?
SPQR meant Senatus Populusque Romanus in Latin, which translates to “The Senate and the People of Rome.” When imprinted in standards, it represented the Roman Empire and its citizens, particularly when carried by legions.
SPQR was the closest thing to a representative symbol of the Roman Empire. The earliest records of the symbol date back to 80 B.C., but perhaps it was in use before that.
The letters are an abbreviation of Senatus Populusque Romanus, referring to the two powers of Rome: the Senate and its citizens.
SPQR can’t be said to be the Roman flag because it didn’t represent every Roman territory. The Empire encompassed wildly different cultures, many of which had little in common with the city of Rome.
Most of the people living under the Empire weren’t considered citizens.  In fact, for most of the Empire’s existence, only people from Rome and neighboring regions had citizenship.
The Senate was supposed to represent the interest of Roman citizens, but this clearly excluded much of the Empire. In practice, each province had fairly autonomous governance.
The only thing that could bring symbols like SPQR and the Aquila to every corner of the Empire was the Roman army.
Also see Did the Romans Know About America? to learn more.
When and Where Did Roman Standards or Banners Appear?
The first Roman standards were called maniples and appeared before 315 B.C. in southern Italy. After 105 B.C., a sculpted eagle became the standard for all legions across the Empire. Centuries, one of the subdivisions of a legion, carried personalized standards with animals and other symbols.
The first Roman standards were made of bundles of straw or fern tied to a pole. These makeshift ensigns fulfilled the role of identifying a group of soldiers, differentiating them from the enemy and keeping them together.
After some time, each manipulus —the group of soldiers gathered under a specific banner— started to take on animals as their symbol.
Thus, five animals became the norm for the standards of Roman legions:
- The eagle
- The bull or minotaur
- The wolf
- The horse
- The boar
Meanwhile, cavalry units emblazoned symbols of serpents or dragons. 
Starting in 104 B.C., customs regarding standards changed. Four of the five animals were left aside, and only one remained: the eagle. The eagle came to represent the Senate, which was, at least in theory, the ruling power of the Empire and representative of its people.
This later form of the standard wasn’t a piece of fabric hanging from a pole. The eagle standard, which came to be known as the Aquila, was a sculpted eagle made of silver, bronze, or gold, sitting on a wooden pole with extended wings.
Each Roman legion had its own Aquila. The soldier in charge of carrying it was called the aquilifer. It was considered a position of honor since he would be in charge of giving courage to the rest of his legion.
Often, a banner called Imago was displayed under the Aquila. The Imago showed a portrait of the current emperor, and it was a way of reminding the soldiers who they were fighting for.
However, Aquilas weren’t the only standards in a Roman army. They were the regular standards for legions, but legions were the highest-level group of an army.
A legion was composed of ten cohorts, each containing 480 soldiers. Each cohort was then subdivided into five centuries, which contained 80 men each. Even though they weren’t as fancy as Aquilas, centuries had their own emblems.
The standard carried by a century was called a Signum. Each Signum was carried by the signifier, who usually wasn’t a soldier and didn’t truly participate in battle.
Unlike a legion’s Aquila, Signa were varied in color and shapes. Sometimes they took on the Zodiac sign of the century’s inception or their commander’s birth.
There was a third standard commonly used by Romans in battle: the Vexillum. This banner served a more practical purpose. It had specific numbers and colors that designated the kind of unit —legion, cohort, century, etc.— and the larger group of which they were a part.
The Roman Empire was vast and diverse. Its regions were so different that having a single flag for all of them would’ve seemed absurd.
Also see Did Romans Steal Greek Gods? to learn more.