““The black ash that inundated the island was suitable for a superior quality of concrete, and the resulting caves, bunkers, pillboxes and large rooms were elaborate. Up to one quarter of the entire garrison was enlisted in the tunneling, and while some of the caves were suitable for two to three men with gear, others could hold up to 400, with multiple entrances and exits to prevent forces from becoming trapped. Ventilation systems were engineered to contend with the danger of sulfur fumes common to the island. On Mount Suribachi itself, the 60 foot-deep crater with a 20 foot ledge on which one could walk the entire circumference of the rim was particularly well-developed as a fortress. The Japanese had constructed elaborate caves all the way around the crater, and according to one of the 28th Marines who took the summit, “It was down in the crater that the Japanese were honey-combed.”[3]””
![“[At Gunung Padang] First, the drill cores contained evidence--fragments of worked columnar basalt--that more man-made megalithic structures lay far beneath the surface. Secondly, the organic materials brought up in the drill cores began to yield older and older dates--3000 BC to 5000 BC, then 9600…” quote by Graham Hancock](https://sms4smile.com/quotes/img-quotes/19f/graham-hancock-10752_archeology_at-gunung-padang-first-the-drill-cores-c_3047699.jpg)
