The historic core of Farnham is sited on the linear gravel terrace that lies immediately to the north of the River Wey within the relatively steep sided southwest/north east valley carved by the river. The underlying geology consists of Gault clay and Upper Greensand while to the north the town is bounded by a chalk ridge and land rising to a height of about 160m. This geology and topography has had a profound effect on the development of the town throughout its existence, limiting its expansion, until recently, to the north and south, but encouraging ribbon development along the line of the valley. The town has prospered because of its position, about half way along the road between London and Winchester, and at the point where this is joined by a route from the south that crosses the Wey at what is now Longbridge.
While there is little evidence for direct occupation of what is now the centre of the town before the Saxon period, the Wey valley and surrounding countryside are extremely rich in prehistoric sites. The area is famous for the many Palaeolithic axes, dating up to 600,000 years ago, that have been found in the various gravel terraces. Other finds from the later part of this period within and close to the town centre include the remains of mammoths, woolly rhinos and evidence for permafrost cracking from the last ice age. More recently there are numerous Mesolithic sites, dating from approximately 10,000 years ago, including several known within the town itself. Evidence from the Neolithic, Bronze and Iron Ages indicate ever-intensifying occupation and exploitation of the better soils within the river valley.
Romano-British occupation took the form of small scattered settlements, many of which appear to be associated with the production of pottery, as a number of kilns have been found, particularly to the south of the town. In the latter part of the Roman period a small villa was built just under a mile north-east of what is now the town centre. There is, as yet, no evidence for direct occupation underlying the town, but a number of sherds of Roman pottery have been found on various development sites. These probably represent manuring scatter from agricultural activities perhaps centred on the villa itself. It is also probable that the Roman road from Winchester to London passes somewhere close to the town, though perhaps slightly to the north of the current centre.