The most serious restriction on economic growth in Byzantium was that the main unit of agricultural production, the peasant holding, was geared mainly to its own reproduction. Its resources for making improvements to its property were limited and the most obvious way of increasing production was simply to extend the area under cultivation. The peasant household's other major objective was to produce enough to meet the obligations imposed by the state or a private landowner. The larger amount of money which was being extracted from the rural economy corresponded either to a more effective exploitation of agricultural resources or to higher prices caused by a stronger demand for food from towns. Unfortunately, there is an almost complete dearth of grain and other prices during the period. Any consideration of agricultural production is fraught with difficulties owing to the deficiencies of the evidence. No figures of crop yields survive from this period. The only surviving treatise on agriculture is the Geoponika, a reworking of a sixth-century compilation, which consists of extracts from classical authorities. There is no indication of any advances in agricultural technology, but it is equally important to consider how effectively agricultural resources were exploited within the limits of the technology available to the Byzantines and what effect the social trends of the period had on agricultural production. There has been a tendency to regard Byzantine feudalism as a negative factor leading to economic decline, but as the revenues of large landowners increased they had greater resources to make improvements to their properties.