As France began to pose more of a military threat to England, the strategic importance of Portsmouth grew. In 1689, Parliament ordered a new dry dock to be built there, large enough to accommodate the latest first-rate and second-rate ships of the line (which were too big for the existing docks). Work began in 1691; as with all subsequent extensions to the dockyard, the new works were built on reclaimed land (on what had been mud flats, to north of the old double dock) and the civil engineering involved was on an unprecedented scale.