The ancient city of Aquincum was situated on the North-Eastern borders of the Pannonia province within the Roman Empire. The ruins of the city can be found today in Budapest, the capital city of Hungary. It is believed that Marcus Aurelius may have written at least part of his book Meditations at Aquincum. Originally settled by the Eravisci, a Celtic tribe, and named Ak-ink (“Abundant Water”) because of the nearby thermal springs, Aquincum served as a military base ( castrum ), having been part of the Roman border protection system called " limes ". Around AD 41-54, a 500-strong cavalry unit arrived, and a Roman legion of 6000 men was stationed here by AD 89. The city gradually grew around the fortress, and after Pannonia was reorganised by the Romans in AD 106, Aquincum became the capital city of Pannonia Inferior. The city had around 30,000 to 40,000 inhabitants by the end of the 2nd century, and covered a significant part of the area today known as the Óbuda district within Budapest. Ruins from the old Roman settlement can be seen in other parts of Budapest as well, notably Contra-Aquincum and the Amphitheater. People living in the settlement could enjoy the achievements of the Empire, like central heating in the houses, public baths, a Mithraeum and palaces, as well as amphitheatres for gladiatorial combats and beast fights. Many historic artifacts from the city now appear in the Aquincum Museum.