The date and mode of the introduction of agriculture into the Japanese archipelago continue to be an area of vigorous debate.

The early Japanese archaeological sequence is divided into ‘Palaeolithic', ‘Jomon', and ‘Yayoi' periods, and the division between the Jomon and the Yayoi is defined by the presence of agriculture.

The technology of wet rice farming was introduced into Japan from the EastAsian continent, firstly into northwestern Kyushu shortly after 1000 bce. Some of the most extensive areas of prehistoric rice paddy discovered to date are in the Nara basin, although no paddy sites in this area yet extend as far back as 1000 bce. These sites in the Nara basin are, however, very informative about the spread of rice farming through the western part of the Japanese archipelago, and about the associated transition from the Jomon to the Yayoi period of Japanese prehistory. The site of Kashiwara is one of the most important Jomon sites in the area, providing the ceramic chronological sequence for the end of the Jomon.^{[805] [806]} The enormous quantities of tools discovered at Karako-Kagi since the 1940s demonstrated unequivocally that the Yayoi period was agricultural.^[807] Discoveries in the Nara basin have proved that paddy facilities were present between 2,600 and 2,400 cal bp, in the early Yayoi period.

Rice paddy technology was not invented in the archipelago, but spread into Japan from the Chinese mainland through the Korean peninsula. Recent archaeological investigations in Nara prefecture are adding greatly to our understanding of the spread of rice farming through Japan, even though the Nara evidence postdates the initial arrival of wet rice farming into northwest Kyushu by several centuries. A number of new sites have been excavated, dating from the middle of the early Yayoi period, about 2,500 years ago. These excavations have revealed a massive area of planned rice paddy, over 25,000 m² in area, complete with the irrigation systems needed for its opera­tion. Findings from these sites suggest that wet rice cultivation began in this area relatively suddenly, and continued despite a number of natural disasters. These sites therefore offer the possibility of understanding the conditions under which wet rice farming spread through this part of Japan.