Created during the Roman era, the vineyards of Chablis flourished between the 9th and 12th centuries, thanks to monks of Saint-Martin de Tours, followed by Cistercians from the abbey of Pontigny. In 867 Saint Martin's followers were bequeathed land and started vineyards on the hillsides just across the river Serein. This is clearly the historical heart of Chablis' vineyard, and forms the site of today's Grands Crus. In 1118, monks from the abbey of Pontigny rented a vineyard in Chablis from the monks of Saint Martin de Tours. From the 13th century, the importance of Chablis' wines increased, both geographically and commercially. They became a major contributor to the town's budget By 1328, the vineyard was estimated at 500 hectares, divided amongst 450 different owners. The wines travelled by road to Auxerre, then going down the river Yonne, reaching Paris, and ultimately Rouen for export towards northern Europe. Comments of the time, such as "...as clear as spring water", "...keeps excellently", show Chablis' specific status amongst French wines. In the 18th century, whilst the rest of the Yonne extensively planted other varieties producing higher yields but of lower quality, Chablis' vinegrowers remained true to the Chardonnay grape that had established the renown of their wines. It was the perennity of this quality, linked to a relative shortage of fine wines, that created the reputation of Chablis. Throughout France, the revolution modified land tenure and Chablis was no exception. Church belongings were confiscated and sold to private individuals. Thus, large tenures were divided between the local bourgeoisie. Success continued through the first part of the 19th century. Through the previous centuries, vineyard surface had remained fairly stable. It now started to spread from the immediate vicinity of the town of Chablis, well beyond its contemporary limits, to encompass up to 38,000 hectares. This placed the Yonne on the leader-board of France's wine-producing departements. The first sign of future troubles came with the arrival of the railways. France's rapidly developing railway network allowed large volumes of wines from the south to be transported to the major markets quickly and at a reduced cost. The second half of the century saw a series of natural catastrophes : in 1886 powdery mildew struck, followed by phylloxera the following year. The vineyards were decimated, and although replanting started in 1897, the Yonne vineyards had receded by 45%. Luckily, in Chablis, the drop was much lower thanks to the individual character and intrinsic quality of its wines, for which no "substitutes" could be found. By 1902, Chablis vineyards had lost just 15% of their surface area. Because of their prestige, the wines were often imitated, and the first frauds were found in 1898. This caused growers to get together in order to organise the defence of their wines, and raised the question of precise definitions, geographic and other, of what constituted "authentic" Chablis. There were diverging viewpoints on the subject. Was the presence of the sole chardonnay variety a sufficient criteria of "authenticity", or should there also be a soil factor, such as the presence of kimmeridgian limestone ? And how should the vineyards be ranked, and on what basis ? In 1919 a consensus was reached on a small number of vineyards sites that had been known and observed over centuries : Vaudésir, Grenouilles, Valmur, Les Clos and Blanchots. In 1938, Preuses and Bougros (initially spelt Bouguerots) joined them, forming the appellation Chablis Grand Cru with its seven individual sites, or "climats".     Les Clos