Most landforms which we see now do not reflect excludingly the results of natural forces. They were formed in various times of the past by pure natural processes, by natural processes affected by man and/or throughly by human activities, and they were later in some measure modified.<br> In the Sekkasen region in Osaka Prefecture mentioned here, landform transformations were remarkable from the 5th to the 12th century. They are summarized as follows;<br> Many of the small old tombs are located on the tops of hills, on the ridges of lower hills and upper terraces. On the contrary, most of the big old tombs, the biggest of which amounts to 10⁶m³ in volume, were constructed on middle and lower terraces. The direct transformations by the construction of old tombs were excavation and accumulation of soils, and the secondary transformations were coused by soil erosion, increase of the width of rivers and of the volume of sediments, changes of river courses and so on.<br> Next, ruins of the kiln of the “Sue-ki” were extensively distributed on the hills and the terraces. In case of the Senpoku Hills, 70% of the ruins of the kilns are concentrated on the slopes of hills and the cliffs of terraces. By construction of these kilns, not only landforms but also vegetation were remarkably modified. As the concentrating area of the ruins of the kiln coincides with the area of the Senpoku New Town, about 80% of these ruins were destroyed and disappeared by the construction of roads and housing lots.<br> The aim of the construction of huge reservoirs and ditches in this region was to irrigate the terraces. While the reservoirs were built in the lower to upper reaches of the rivers, the ditches were dug to conduct water of the east rivers to the terraces of the west. At the middle of the 5th century, the middle terrace, where the relative height from the flood plain was the smallest, was chosen to construct a reservoir, and at first the “Yosami-ike” Reservoir was constructed. Its aim was to reserve temporarily the water of the former Amano River and dissected valleys which cut into the terraces, and to send water to the lower reaches of the river afterwards.<br> The “Hario-no-taiko” Ditch was constructed at the middle of the 6th century mainly to conduct water of the former Tsuzuyama River into the middle terrace of the west. The excavated length on the terrace amounted to 2, 000m, and the irrigable area was about 550 ha. Further, the “Komuku-no-taiko” Ditch was constructed about the end of the 6th century for the same purpose. Total length of the ditches was about 6, 000m, and the irrigable area on the terrace was about 300 ha.<br> The “Sayama-ike” Reservoir was constructed by damming up the whole valley plain formed by the former Amano River at the beginning of the 7th century when exploiting of terraces of the lower reaches was in advance and the need to irrigate the upper reaches of the river became pressing. It is considered that at the beginning of the construction the length of the north bank was about 300m and the area of the reservoir was about 20 ha. It was, however, enlarged to more than 50 ha in 1608. It took today's shape by the reconstruction of it in the 1920's. In addition to this, with construction of the reservoir, the “Yoge” Ditch was dug as a draining ditch extending over 1, 000m in total.<br> By introduction of the “Jon” grid-system, an ancient land division system, not only the lands with micro-reliefs were levelled, but also old dissected valleys, irrigation and draining ditches, footpaths separating rice fields and so on were arranged in order.