The three outer island of the present Krakatau group (Rakata, Seretung and panjang) are thought to be the remnants of one previous, huge volcanic island. Called "Ancient Krakatau", it was some 11 km in diameter and 2 km high according to records in the Javanese "Book of kings" it exploded and collapsed, perhaps in prehistoric times but possibly as recently as 416 AD. Three island remained on the rim of its submerged, 7 km diameter, central caldera (Collapsed crater). The south easternmost of these, Rakata, grew by volcanic activity until it was about 830 m high and 5 km in diameter. Two smaller volcanic island, Danna (450m) and Perbuatan (120 m), then developed in line and to its north, within the ancient Caldera the three island later joined up into one, Krakatau volcano Indonesia. This was about 9 km long and 5 km wide (dashed line in fig.3). There are records of seven eruptions of Krakatau between the 9th and the 16th centuries. By the nineteenth century it was regard ed as Dormant.