The development of the Carolingian economy was fueled by the efficient organization and exploitation of labor on large estates, producing a surplus of primarily grain, wine and salt. In turn, inter-regional trade in these commodities facilitated the expansion of towns. Archaeological data shows the continuation of this upward trend in the early eighth century. The zenith of the early Carolingian economy was reached from 775 to 830, coinciding with the largest surpluses of the period, large-scale building of churches as well as overpopulation and three famines that showed the limits of the system. After a period of disruption from 830 to 850, caused by civil wars and Viking raids, economic development resumed in the 850s, with the emporiums disappearing completely and being replaced by fortified commercial towns.