In 1703 territorial waters were defined as extending out to three nautical miles of the coast - the distance that could be covered by a cannon shot. In 1958 the Geneva Convention introduced the concept of baselines from which all other measurements would begin. Baselines were to be smooth and parallel too, rather than following the detailed indentations of the coast. Baselines join headlands and may run to the low-water mark of islands. All waters - marine and transitional (estuarine) on the landward side of baselines - are part of the internal (inland) waters of the State. The territorial sea extends out to 12 nautical miles from the baselines. The Irish Republic territorial sea covers an area of 27,487 km squared. The area covered by internal waters is 13,650 km squared.