Arechis I (also Arigis, Aretchis, Italian: Arechi) was the second duke of Benevento from 591 to his death in 641, a reign of half a century. He was from Friuli and was a relative of the dukes there, maybe a nephew of Zotto, his predecessor. He was appointed by King Agilulf in the spring of 591, after Zotto's death. He was practically independent because his duchy was separated from northern Italy by a stretch of Byzantine territory.
He conquered Capua and Venafro in the Campania and areas of the Basilicata and Calabria. He failed to take Naples after a siege (Zotto had failed likewise), but he took Salerno by the late 620s. He spent the last years of his reign establishing good relations with the Roman Catholics of his duchy and making his son his successor. On his death, having survived many a king, his independence was assured and his domain passed to his son Aiulf.