sentences:  Work began in 1370 with another pair of towers being built behind the first bastille, followed by two towers to the north, and finally two towers to the south.The fortress was probably not finished by the time Charles died in 1380, and was completed by his son, Charles VI.The resulting structure became known simply as the Bastille, with the eight irregularly built towers and linking curtain walls forming a structure wide and deep, the walls and towers high and thick at their bases.