The Lavaux vineyards include nearly 450 kilometres of walls in total and the surface area of the walls is as great as that of the vines! These walls, which make it possible to build terraces that are less steep and therefore able to hold vines, are built of stones that are generally found nearby (for example, from rockslides). They are held in place by a chalky mortar. At the top of the wall, there is usually a horizontal line of large flat stones. This helps reduce rainwater slipping in and ensures a longer life for the wall. The walls also offer the advantage of giving back, during the night, the heat they have accumulated during the hot daytime hours.