Written sources of the Early Middle Ages mention only one merchant port, located on the Eastern coast of the Baltic sea – the Semigallian port (portus Semigallia), which belonged to proud and wealthy Semigallians. At that time, as one of the most warlike and wealthiest nations in Northern Europe, Semigallians controlled the two biggest rivers of the contemporary Latvia – Lielupe and Daugava. „Portus Semigallia” was the biggest port of the region and Semigallians were known as resourceful merchants and brave mariners. No written source mentions any other port, which belonged to any of the local Baltic or Finno-Ugric nations in the Early Middle Ages or the previous epochs. Zemgalian port is mentioned in the Livonian Chronicle of Henry (13th century).
The location of such an important ancient port has not been revealed up to this day. Historians searched it on the banks of Lielupe and Daugava. Some researchers presume, that it could be located in the estuary of Lielupe or in the surroundings of Jelgava, or in Mežotne, while other believe that it could be located in Daugmale or Daugavgrīva. After a persistent claim by Teodorich - bishop’s Albert’s brother and aide, in 1200 Roman Pope Innocent III prohibited Christian merchants to enter the port. Also, in order to secure the prosperity of Riga, local merchants announced that anyone, who would dares visit the port with the purposes of trade, will be deprived of his goods and, even, life. Some years after this prohibition the Germans arrested merchants, who were heading to the Semigallian port. Ship’s captain and pilot were executed, while the rest of the crew was forced to return home.
Logically seems that if Semigallians had their own port and trading houses in Europe, than they must have obtained their own navy. References to the Semigallian port in the written sources is a fact of considerable significance, which serves as an evidence of its important regional role. Also, the above-mentioned events of the 13th century prove that Semigallian port had a strong competition with Riga and even served as an obstacle to its prosperity. Considering the active trade of Semigallians with their neighbors and Europe, it is logical that they had their own port, which existed long before the 13th century and disappeared with the beginning of the Crusader Wars in the Baltic region.
Tales and sources tell us, that successful Semigallian port was frequently visited by Viking merchants from Northern Europe. This is proven by the runic stone from Mervall, on which the following words are engraved: ”Sigrida ordered to put this stone in memory of her husband Sven, who often travelled with rich ships to Semigallia around the cape of Kolka”. According to the research by Richards Ērgļis, the ancient “Semigallian port” was in the estuary of the main nerve center of Semigallia – Lielupe, even though the inhabited part of the settlement has not been indubitably determined. Starting from the 19th century and till the 21st century, archaeological excavations in Mežotne had been carried out six times, however, they did not reveal the location of Semgallian port. Research works of a wider scale have not been carried out at the foot of Mežotne hillfort for the last 47 years.