Without doubt, it was the light from fires of people living by the shore that acted as navigational aids to ancient mariners. Once a fire had been deliberately set to help mariners find their way home, then the first lightstructure or beacon had been created.
At Skagen in Denmark, a replica of a device called a vippefyr has been constructed. This was used to raise and lower a brazier full of burning materials, usually coal.
Figure H01: A replica of a device called a vippefyr at Skagen in Denmark.