Abstract
　It is found that in japan composite breakwaters have been exclusively constrcted, while in other countries rubble mound breakwaters are very popular. This discrepancy is quite clear. The principles of breakwaters were established in Europe around l850. At that time, wave motion in water was of course still incompletely umderstood. The established priciples are as follows; a vertical wall reflect waves and a sloping wall absorbs wave energy through its breaking. The Yatoi who were hired foreigners had introduced the technology of breakwater construction in early modern Japan. It is pointed out that composite breakwaters have been widely used in our country since about 1900 and because it has been improved the vertical wall can control boyh wave forces due to breaking and reflection.

【キーワード】：防波堤, 混成堤, 傾斜堤, 直立堤, 海岸災害, 風土, お雇い技師, 災害技術史, 明治維新

*京都大学防災研究所
Disastr Prevention Research Institute, Kyoto Univ.