The Gangani were a people of ancient Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 who are referred to in Ptolemy

Ptolemy

Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

's 2nd century Geography as living in the south-west of the island, probably near the mouth of the River Shannon

River Shannon

The River Shannon is the longest river in Ireland at . It divides the west of Ireland from the east and south . County Clare, being west of the Shannon but part of the province of Munster, is the major exception...

, between the Auteini to the north and the Uellabori to the south. There appears to have been a people of the same name in north-west Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

, as Ptolemy calls the Llŷn Peninsula

Llŷn Peninsula

The Llŷn Peninsula extends into the Irish Sea from north west Wales, south west of the Isle of Anglesey. It is part of the modern county and historic region of Gwynedd. The name is thought to be of Irish origin, and to have the same root Laigin in Irish as the word Leinster...

the "promontory of the Gangani" (Γαγγανὤν ἄκρον).