Around 41 to 55 AD, a 500-strong cavalry unit, or
alae, was stationed at the site. This was soon reinforced when an entire Roman legion was sent there no later than 80 AD. This legion comprised a considerable force of around 6,000 men, along with all their military equipment. As the fortress grew in size, so too did the city surrounding it expand to become a city of import.
The province of Pannonia was crucial to the Roman Empire, providing the Roman Army with a secure base. It was also close to the river Danube which was a tactical location allowing the Roman Navy access to patrol the banks of this critical waterway. By 106 AD the Roman Empire decided to bring about changes in Pannonia and Aquincum became the capital city in the region they now called Pannonia Inferior.