People used to pray in Sumiyoshi-taisha Shrine in Sumiyoshi Ward, Osaka, for safety of the ships for mission to Tang China, and put 'Sumiyoshi-Daijin,' the alter of the god of the sea, on the bow of the ships; they left Suminoe no tsu (Suminoe Port) (Sumiyoshi Ward, Osaka City) and entered the Osaka gulf from Hosoe in Sumiyoshi (current Hosoe-gawa River, commonly called as Hosoi-gawa River; Hosoigawa Station), stopped over in Naniwa no tsu (Naniwa Port) (Chuo Ward, Osaka City) and arrived at Nanotsu (Fukuoka City in Fukuoka Prefecture) via Seto Island Sea.
遣唐使船は、大阪住吉区の住吉大社で海上安全の祈願を行い、海の神の「住吉大神」を船の舳先に祀り、住吉津（大阪市住吉区）から出発し、住吉の細江（現・細江川。通称・細井川。細井川駅）から大阪湾に出、難波津（大阪市中央区(大阪市)）に立ち寄り、瀬戸内海を経て那の津（福岡県福岡市）に至る。