Definition of mare liberum in US English:

mare liberum

nounPlural maria libera

  • The sea that is open to all nations.

    • ‘As to peacetime naval presence - and as a matter of principle - the Baltic Sea must be considered a mare liberum.’
    • ‘The Hudsoninn Sea, according to the facts as expressed by Mr. Gordon in his above cited opinion, was in 1893 a mare liberum.’
    • ‘In Chapter 3 and later in his treatment of the Dutch, Barendse makes clear the tension between the perception of the Atlantic Ocean as mare liberum where all vessels are free to trade in times of peace and the perception in other seas.’


Latin, literally ‘free sea’.


mare liberum

/ˌmärā ˈlēbəro͝om/