Causantín or
Constantín mac Cináeda (in
Modern Gaelic,
Còiseam mac Choinnich; died 877) was a
king of the Picts. He is often known as
Constantine I in reference to his place in modern lists of
kings of Scots, but contemporary sources described Causantín only as a Pictish king. A son of
Cináed mac Ailpín ("Kenneth MacAlpin"), he succeeded his uncle
Domnall mac Ailpín as Pictish king following the latter's death on 13 April 862. It is likely that Causantín's (Constantine I) reign witnessed increased activity by
Vikings, based in
Ireland,
Northumbria and northern
Britain. He died fighting one such invasion.