The Amsterdam Canal was built to connect Amsterdam with the sea. Formerly, ocean-going vessels were small and the Zuider Zee River was then a stream of considerable depth. Gradually, however, the Zuider Zee became shallower and the size of ocean vessels larger, so that the commercial supremacy of Amsterdam was threatened by the competition of Rotterdam and Antwerp and north German ports. In 1818 a corporation constructed what was known as the "North Holland Canal," which was large enough to accommodate ships employed in the East India trade. It had a minimum depth of 20 feet and a minimum width of 100 feet. This canal, however, had numerous curves and it was constructed by a roundabout route of 52 miles from Amsterdam northward to the North Sea, while Amsterdam is less than 17 miles from the sea by direct route. In 1863 a concession for the construction of the North Sea Canal was granted and two years later active work began. It was finished in 1876. There were no serious engineering difficulties to be met, there being no rivers to be crossed, no towns to block the way, and only three bridges to be built. The work consisted mainly of building embankments, draining and reclaiming land, and dredging the channel. The canal was not completed according to the original plan. Extensive enlargements and improvements were decided on, and a larger additional lock was undertaken in 1889 and completed in 1896. At that time it was the largest canal lock in the world. Plans are now being considered for building another new lock, which will be larger than those at Panama. The bottom width of the canal is now 164 feet. It can accommodate vessels 721 feet long, with a 79-foot beam and of 30 feet draft. The construction of the canal cost $16,000,000. Improvements have brought the total amount up to about $24,000,000. Since 1893 all toll charges have been eliminated, and the canal has been operated at the expense of the State. The annual average cost of operation and maintenance is about $200,000. This canal bears about the same relation to the city of Amsterdam that the Delaware River Channel bears to the city of Philadelphia, or the improvements on the lower Mississippi to the city of New Orleans. The Cronstadt and St. Petersburg Canal is 16 miles long and gives St. Petersburg an outlet to the Gulf of Finland. It was built at a total cost of about $10,000,000. It has a minimum width of 220 feet and a navigable depth of about 20-1/2 feet. It was built primarily as a military undertaking, but has proved of great service to Russian commerce. Another important European canal is that extending from the Gulf of Corinth to the Gulf of Aegina in southern Greece. Its length is about 4 miles, a part of which was cut through soft granite rock and the remainder through soil. It has no locks. The bottom width is 72 feet and the depth 26-1/4 feet. The average tolls are 18 cents per ton and 20 cents for passengers.