I apologize in advance for any mistake, English is not my first language. Caesar arrived in Alexandria in October 48, following Pompeus. Not only was Pompeus already dead (he was killed by the Egyptian government) but he really ended up stuck in Alexandria for 9 months during what was basically a civil war between the Cleopatra and her husband, her younger brother Ptolomey who had very good advisors. They were fighting for the throne since neither of them wanted to rule with the other. How and why exactly Caesar decided to take a side in this civil war was already a problem for ancient historians: some believed it was because he loved Claopatra, others thought that the advisors of Ptolomey truly believed they could kill both Pompeus and Caesar. Theodore Momsen wrote that Caesar would simply have liked to resolve the Egyptian situation as soon as possible, convincing Claopatra and her brother to make peace and also taking the money Egypt owed Rome. Caesar decided on his own to take residence in the palace (don't think of an actual palace, think more of a whole neighborhood of the city) since it was one of the easiest place in the city to defend. He did not trust Alexandria at all, since it was by all means a time bomb. He took Cleopatra' side in the civil war, maybe because of their relationship but there's the fact that he considered Cleopatra a more trustworthy ally to Rome so it was auspicabile to have her reign with his brother (since getting rid of him was a bit more tricky) , while Ptolomey and his advisors where more anti roman, or rather they were clever enough to understand the precarious situation in Rome caused by the civil war between Caesar and Pompeus and were hoping to gain more independence. So Caesar end up stuck in the palace of Alexandria with the young king, who was effectively his hostage while the city was rioting because they did not like Caesar, they did not like Rome, they hated the fact that they had to pay money to Caesar and they also hated Cleopatra. Ptolomey's advisor marched with the army towards Alexandria and laid siege both to the palace and the harbor. The siege to the palace was blocked but the one to the harbor was truly dangerous for Caesar since it would have cut off any eventual help. So Caesar decided to do what it's probably the most famous thing of the Alexandrian War, he burned down the ships, the harbor and even the neighborhood near the harbor (but he did not burn the library of Alexandria!! That was inside the Palace where Caesar was). This war lasted for some months, king Ptolomey was eventually released by Caesar, the final battle was between an army mailny formed by Jewish people under the command of Mitridate and Antipatrus (sorry I have no idea what they're calles in English!!) who arrived to help Caesar and Ptolomey's army. Ptolomey was killed in battle. Hopefully you will understand something out of my ramble. Caesar's involvement in the civil war in Alexandria was one of the most risky and messy part of his whole military career, there was a moment where he was truly stuck and risked his own life. Edit: as you can see though it wasn't Ptolomey holding Caesar hostage, it was more Caesar holding young Ptolomey hostage inside his own palace!!