We analyse the integration of wheat markets across 18 towns in the Austrian Low Countries during the second half of the 18th century and the relationship with the rapidly expanding paved road network in this period. We use a switching regression approach (threshold cointegration) to study long-run and short-run integration of these markets, using monthly wheat prices. We find that throughout this period, markets were spatially interconnected. However, price margins adjust only slowly to long-term levels in response to local shocks. We also find that transaction costs are relatively high. The results suggest a complex market with regular trade flow reversals and periods of unprofitable trade between key markets. It is widely accepted in Belgian historiography that the construction of a paved road network caused a substantial reduction in transaction costs. Our research, however, indicates that distance, fixed costs or links by rivers and canals mainly influenced transaction costs, not the expansion of a paved road network. Two factors can account for this. First, the toll structure on paved roads discouraged bulk trade. Secondly, new private investment in inter-city grain trade that may have led to cuts in the trading costs, typically appeared to be absent in this period. However, adjustment speeds in markets are significantly affected by the existence of paved roads. Better communication and faster transport due to the road network resulted in faster arbitrage.