He Spread Roman Influence Throughout Europe 

Caesar's conquest of Gaul, consisting of modern-day France and Belgium, as well as parts of Switzerland, Germany, and the Netherlands, was crucial for spreading Roman influence throughout Europe. It added not only a substantial amount of land to Rome’s holdings, but also wealth. 

In 55 BCE, the relentless Roman general led his first of two expeditions to Britain. While neither that nor the second trip the following year was successful at taking over the land, the expedition laid the foundation for Rome to eventually conquer much of the British Isles. These conquests weren’t just about land and riches — they were all part of Caesar's ultimate political ambitions. By increasing his military support and popularity with the people, Caesar set the stage for his pursuit of more power in Rome. As he conquered more regions, he integrated the republic’s legal and political systems and increased trade by expanding the network of roads leading in and out of Rome. The famous bridges Caesar built on the Rhine River during the Gallic Wars are just a few of many aqueducts ancient Rome is known for.

He Introduced the 365-Day Calendar

In 46 BCE, Caesar, advised by the Greek astronomer Sosigenes, reformed the Roman calendar. The traditional calendar was based on the phases of the moon and was often out of sync with the solar year. The new system, influenced by the Egyptian calendar, was based on calculations of a solar year of 365.25 days. The calendar was divided into 12 months, with an additional day added every four years to ensure the calendar stayed in line with the Earth’s orbit around the sun. The Julian calendar — named for its progenitor — was implemented on January 1, 45 BCE.

The calendar became the predominant timekeeping system in the Western world, but the calculations were just a little bit off — the solar year ran about 11 minutes shorter than expected. By 1582, the miscalculations had added up to a 10-day discrepancy. It was rectified by the Gregorian calendar, modified by Pope Gregory XIII and introduced in 1582, but the Julian calendar’s standardized method of measuring time continues to structure our lives to this day.

He Changed Political Strategy

Caesar’s political ambition and reforms had an enduring impact on political thought and practice in Rome and beyond. One of his most powerful strategies was cultivating support from common Roman citizens, as well as his army, as a means of gaining popularity that would bolster his rise to power. 

After naming himself the republic’s dictator, he made a number of revolutionary political reforms: He supported redistributing land to go to veterans or to the poor, canceled debt and rent payments for a period of time, and planned a public library, to name a few. His populist approach worked. After his death, the Senate granted him divine status, making him the first historical Roman to achieve the status. 

He Inspired a Shakespeare Play

Caesar was hailed as a master orator in his time, but he was also a celebrated author. His writing style, which was praised for its clarity and elegance, lives on in very few published works; his war memoirs, Commentarii De Bello Gallico (an account of the Gallic Wars) and Commentarii de Bello Civili (an account of Rome’s civil war), are the only surviving primary texts. His Gallic Wars account in particular is popular not only for its insight into Roman geographic and military history, but also as a beginner’s guide to learning Latin.

Of course, it isn’t just his own work that lives on: Caesar’s remarkable rule inspired one of the most famous works by one of history’s greatest playwrights. Julius Caesar, by William Shakespeare, is an enduring classroom and theatrical favorite, and remains a popular point of reference from which to explore one of history’s most influential rulers.

Zenobia

Zenobia’s rule as the queen of the Roman colony of Palmyra (present-day Syria) lasted for only a few short years, from around 267 to 272 CE. During that time, however, her power was undeniable, and she even posed a threat to the mighty Roman Empire. She took the throne after her husband, Odaenathus, and his eldest son, Herodes, were assassinated. Unlike her husband, Zenobia was not content being a client ruler of Palmyra under Rome’s watchful eye. She defied the Roman Emperor Aurelian and boldly seized control of almost the entire eastern part of the empire, including one of its most valuable jewels, Egypt. Aurelian could not afford to sit back and watch Zenobia’s power grow. He marched on the Palmyrene Empire with his entire army, a force that was simply too strong for Zenobia. She was captured and taken back to Rome in chains. From there, historians differ on her fate. Some say she starved herself to death, while others say she was beheaded, though the happier version has her put on trial but acquitted, after which she married and lived the rest of her life in Rome. 

Theodora

Theodora was born in the fifth century CE in Constantinople (now Istanbul, Turkey) into the lower rungs of society. As a young woman she worked as an actress — a job that at the time was in the same class as prostitution. She later moved to Egypt, where she converted to Miaphysite Christianity. Then, on her return to Constantinople — the capital of the mighty Byzantine Empire (or Eastern Roman Empire) — she met Justinian, the empire’s influential heir-apparent. Dazzled by her beauty, vibrancy, and intelligence, Justinian made her his mistress and they married in 525 CE. Two years later, Justinian succeeded to the throne, and it was soon clear that Theodora and Justinian were ruling as intellectual and political equals. In fact, some believed that Theodora was the true ruler of Byzantium. She oversaw much of the reformation of the empire, including construction projects and the establishment of new laws. As empress, she fought for the persecuted and was one of the first rulers in history to recognize the rights of women. She established laws to protect the rights of prostitutes, gave more power to women in divorce cases, and abolished a law that allowed women to be killed for committing adultery. 

Wu Zetian 

Empress Wu Zetian, also known as Wu Zhao, was the first and only female emperor of China. When she was only 14 years old, she was summoned to join the royal court as an imperial concubine of Emperor Taizong of the powerful Tang dynasty. Upon Taizong’s death, she began a relationship with the new emperor, Gaozong, with whom she had four sons and one daughter. She served as empress consort of the Tang dynasty, and after Gaozong’s death, as empress dowager. She then took the unprecedented action of founding her own dynasty, which she ruled as emperor from 690 to 705 CE. Her rise wasn’t without opposition, but Wu Zetian was certainly not weak — she continued to eliminate her rivals, as she had done throughout her life, including her own relatives. As empress, she was both feared and respected. She governed well and employed able advisers in positions of authority, and by the end of her reign, China had become a force to be reckoned with. Wu Zetian was undeniably a powerful figure, but her legacy remains controversial due to her often extreme methods, which may have included brutally killing people, including her own family members, to serve her own advancement. Whether the accounts of her violent acts are all true, however, remains a matter of historical debate.

Elizabeth I 

In 16th-century Europe, many people believed that a woman wasn’t fit to rule, and the 44-year reign of Elizabeth I went a long way to changing that widely held belief. Having previously been imprisoned in the Tower of London on the orders of her half-sister, Queen Mary I, Elizabeth later ascended to the throne of England in 1558. The kingdom she inherited was relatively small and threatened by internal division. Elizabeth, however, transformed and unified the nation, bringing about a golden age — the Elizabethan age — in which the arts and sciences flourished and England became a true global force. Elizabeth chose not to marry, earning her the moniker the “Virgin Queen,” a decision that partly arose from her unwillingness to compromise her power. She famously defeated the mighty Spanish Armada, and her famous words in 1588 ahead of that battle helped define her position as a powerful ruler: “I know I have the body of a weak and feeble woman; but I have the heart and stomach of a king, and of a king of England too.” 

Catherine the Great 

Russia’s Catherine II, also known as Catherine the Great, came to power by overthrowing her own husband, the neurotic, obstinate, and altogether unpopular Peter III. (He died eight days after he was removed from power, and it’s still not known if Catherine had a role in his death.) Catherine proved to be a highly effective ruler. She surrounded herself with capable advisers — some of whom, most notably Grigory Potemkin, were her lovers — and set about expanding Russia’s borders, adding the territories of Crimea, Belarus, Lithuania, and much of Poland. As a patron of the arts, literature, and education, Catherine led Russia into a new era of political and cultural engagement in Europe. She embraced many of the principles of the intellectual movement known as the Enlightenment, and her court began to attract some of Europe's greatest minds.

Cixi 

The Empress Dowager Cixi is widely considered a cruel and greedy tyrant — although the extent of her cruelties is very much an ongoing debate. What is beyond question is that Cixi was one of the most powerful women in the history of China. She entered the court of the late Qing dynasty as a concubine of the Xianfeng Emperor, with whom she had a child. When the emperor died in 1861, Cixi assumed the role of co-empress dowager, and later took control of the dynasty by installing her nephew as the Guangxu emperor, with herself as regent. In effect, she held supreme power over the empire for 40 years, until her death in 1908. Cixi’s legacy is complex, to say the least. She ruled over a turbulent period, including the Boxer Rebellion and the subsequent foreign invasion of China. And she certainly engaged in political killings. These, by some estimates, totaled a few dozen and included Guangxu's son's favorite concubine and, later, the Guangxu emperor himself. While Cixi was undeniably a powerful ruler, her legacy serves as a reminder of how power can corrupt.