 The city of Saint @-@ Louis , the first capital of the French West Africa , is situated on an island near the estuary of the Sénégal River . It is separated from the Atlantic Ocean by a thin 40 kilometres ( 25 mi ) strip of sand called the Langue de Barbarie , which starts from Nouadhibou in Mauritania and extends all the way to Saint @-@ Louis . The suburbs of Guet Ndar and Ndar @-@ Tout are situated in this area . Until the 19th century , access to the island was by boat . Troops , horses and the equipment of the French colonial army all had to be transported by small boats . 
