On the site, construction started in October 1846, with demolition of the old slaughterhouse, water mills, bazaars and an entire block, and temporary bridges were built on either sides of the old canal, while old curbs and piles were removed from the seabed. Ericson concluded there never was an isthmus connecting the two island, in opposition to later expertise who believe they were cut off around 1000 AD. 2,000 piles were driven into the seabed, one about every two meters, and a bed of grit made up the leveled bed for the caisson. Since the caisson was fit into place the bricklaying of the bottom, sills, and lower parts of the walls began. The caisson was lowered with ballast of gravel and rock waste before water was pored in and the box sank into place — the fit was perfect and the box so tight the planned hiring of a steam engine to pump it dry could be cancelled. As the masonry with mortar begun in May 1849, the ballast was gradually removed. Limestone from Borgholm was used up to 12 feet over the bottom, while granite was cut locally for the upper part of the construction. Between the inner walls of the caisson and the stone walls, homogeneous, well-worked clay was used as a protection against frost and decay, while compressed sand was used outside the caisson. The entire construction was completed in 1850 with the addition of the gates, made in wood below water and iron above, the drawbridges outside the gates, also made of iron, and a cast iron sign was finally added in the middle of the lock displaying: "Built during the VII year of reign of Oscar I". The costs ended at 335,000 riksdaler, 75 per cent below the estimated cost, while the entire project was completed a year before the scheduled five years.