The cliffs of Dover were mentioned by Julius Caesar in his account of the Roman invasion of Britain in 55 BC. Shakespeare too makes reference to them in 'King Lear' and the lines beginning "There is a cliff, whose high and bending head looks fearfully on the confined deep" are commemorated by Shakespeare Cliff to the west of the town.Throughout the centuries, the chalk cliffs have been a symbol of home to Britons abroad and coupled with bluebirds in the popular song of World War II, they provided a world-wide symbol of peace. Although any visitor hoping to see the bluebirds will be disappointed as they were artistic licence on the part of the song writer - obviously bluebirds sounded more romantic than sea gulls! The cliffs were formed in the Cretaceous Period (Mesozoic Era), which commenced about 136,000,000 years ago, and are essentially marine in origin, probably originating in deep, open sea. They consist mainly of upper, middle and lower chalk, i.e. white, soft pure limestone composed of countless shells. The top of Shakespeare Cliff for example, consists of nodular upper chalk with flints, the centre of middle white and nodular chalk and the bottom of chalk (glauconitic) marl and grey chalk on a base of gault and greensand.Numerous fossils have been discovered in the chalk, ranging from shark's teeth, ventriculites, micrasters and many sponges in the upper chalk, to large pectens, palatal teeth oysters, ammonites, remains of saurians and brain corals in the middle and lower chalk. Langdon Cliffs To the east of Dover five miles of countryside and coast are owned by the National Trust. Langdon Cliffs overlook the Straits of Dover and are an excellent place to watch world’s busiest shipping lanes. There is a visitor centre, known as 'The Gateway to the White Cliffs', with a coffee shop and displays about the cliffs.The chalk downland on top of the cliffs is very rare. Many of the plants pre-date the last Ice Age and are adapted to the thin chalk soils and traditional grazing management. Many of the plants are almost unique to this part of Kent.The National Trust continues to graze the chalk downland along the cliff top using Exmoor Ponies. In other areas, where grazing is not possible, a hay cut is taken for the benefit of the chalk downland. The chalk downland supports a rich variety of wildlife. The mild climate makes it an ideal habitat for the Common Lizard and a variety of insects and butterflies are supported by the unique plant communities. Kittywakes, Fulmars and Peregrin Falcons all make their home on the White Cliffs. The sheer cliffs provide a secure nest site, safe from predators. The chalk downland above provides a nesting site for the Skylark.You can walk along the cliff top to visit South Foreland Lighthouse, which is also owned by the National Trust. There has been a lighthouse on the South Foreland for hundreds of years. The present tower was built in 1843 to protect shipping from the Goodwin Sands just off shore. It was from the South Foreland lighthouse, on 28th December 1898, that Gugliemo Marconi made the world's first ship to shore radio transmissions and subsequently the world's first international transmission to Wimereux, in France, 28 Miles away.