Fortaleza del Cerro overlooks the bay of Montevideo. An observation post at this location was first built by the Spanish in the late 18th century. In 1802, a beacon replaced the observation post; construction of the fortress began in <answer>1809</answer> and was completed in 1839. It has been involved in many historical developments and has been repeatedly taken over by various sides. In 1907, the old beacon was replaced with a stronger electric one. It has been a National Monument since 1931 and has housed a military museum since 1916. Today it is one of the tourist attractions of Montevideo.
When did construction of the fortress begin?
1809