Rīga, measuring fifty square kilometers, was the second completely investigated region in Latvia. More than sixty archaeological sites were found in the lower flow of the river Daugava in the flooded zone of the Rīga hydro-station (built between 1966 and 1975). The most important discoveries were in the late Bronze Age fortified settlement and in the burial field, where finds included 247 wooden coffins and evidence of twenty-one cremations under the cultural layer of the Ķivutkalns settlement on Dole island (Graudonis). The first late Paleolithic site near the bank of the Baltic Ice Lake was found in Salaspils Laukskola by Zariņa, and during the excavations flint artifacts of Arensburg and Swiderian cultures were discovered (Zagorsaka). It is currently the only excavated late Paleolithic site in Latvia. The complexes of the Middle-Ages monuments of twelfth- and thirteenth-century stone castles, towns, churches, and cemeteries of the first Livonian bishops, as well as the villages and cemeteries of the local people—the Livs—were discovered in Ikšķile by Graudonis and in Mārtiņsala by Mugurēvičs.

Pļaviņas is a region of concentration of archaeological monuments in the flooded zone of the hydro-station (built between 1958 and 1965) in the middle flow of the river Daugava. Important excavations were carried out at the late Bronze Age fortified settlement in Mūkukalns by Graudonis and at the Letgallian hillfort Oliņkalns of the tenth through the twelfth centuries by Mugurēvičs. Protective investigations of the stone and brick castles of the Rīgas Archbishop and the Livonian order included Koknese (thirteenth through seventeenth centuries a.d.) by Stubavs, and Sēlpils (fourteenth through eighteenth centuries) by Šnore and Zariņa. During the excavations discoveries were made in the towns of the owners of castles as well as in the villages of the local people—the Lettgallians and the Selonians. For the first time in the eastern Baltic, wooden plates and shields with polychrome paintings (white, red, and black) were found in the three graves of Selonian barrows at Lejas-Dopeles (tenth–eleventh centuries).

Sārnate, the first discovered wetland settlement of the Neolithic Sārnate culture, is in the territory of the ancient lagoon of the Litorina Sea. The settlement now lies near the Latvian western coast of the Baltic Sea. The first five wooden dwellings in the peat were discovered by Šturms between 1938 and 1940, and twenty items were discovered by L. Vankina between 1949 and 1959. The dwellings contained a rich complex of wooden hunting, gathering, farming, and domestic utensils. The pottery style represented a special coastal variant of middle Neolithic ceramics and is genetically linked with the pottery of the Ertebolle-Ellerbeck cultures in the west Baltic area (4630–4510 b.p.).

Tērvete was the main political center of the northwestern Semigallians under the guidance of Dux Semigallorum Viesthardus at the beginning of the thirteenth century and Rex Semigalliae Nameisis in the second half of the thirteenth century. The first excavations of the Tērvete hillfort in 1866 and 1892 were by Bielenstein and Hausman. Large-scale investigations were organized in 1930 through 1960 by Emīlija Brīvkalne and a wooden defensive system and previously inhabited plateau inside the hillfort were discovered. Tērvete had the best fortifications of the Semigallian forts at the end of the twelfth century and into the thirteenth century, when the political situation changed and the peaceful development of the Semigallians, as well as the Letgallians, Curonians, and Livs, was interrupted by the crusaders of the Teutonic or Sword Brethren Order. Two defensive systems with two rows of palisades surrounded the hillfort Tērvete and an eight-meter-high rampart was built on the east side of the hillfort. The area of the hillfort was 1,000 square meters and the defensive system included a high log wall along the edge of the hillfort. A double log wall was built in the lower part of the palisade. The defensive system was supplemented by tower-shaped buildings. Special cameras (towers) full of earth and stones were built inside the log walls. In the battle near Saule in 1236 Semigallians conquered the Sword Brethrens Order. It was the end of this order, and some time afterward the new Livonian Order formed from its remains. According to the data from excavations at the Tērvete hillfort and written sources, the hillfort was burned down in 1272. Seven years