The Hisar district of contemporary Bursa was the location of the city of Prusa in antiquity. This district is
located on a wide travertine terrace which slopes steeply upwards towards the Plain, where it is 60 m higher. The
travertine formed via the accumulation of carbonate contained in hot water resources which surface from the
fissures and cracks found throughout the Bursa Fault line, creating a barrier between the metamorphic base and
the neogen. Indeed, the presence of the many water resources found between this travertine terrace and the
slopes of Mount Uludag (Pinarbasi being the most well known) represents one of the most significant factors
influencing the location of Bursa. Another important factor was the need for security. The city was initially
settled within a castle on a high-altitude travertine terrace, but in time has expanded both westwards and towards
the plain over the alluvial cones to the east.