 Complete the following phrase:  In 1682, after Valdivia was badly damaged by a fire it was proposed to move the city to Mancera Island. A similar proposal of moving the city to Mancera Island was done in 1721 in order to protect it against a potential British attack as Spain and Britain were at war. As result of the partial, and eventually reversed move of Valdivia to the island, in the 18th century Mancera Island achieved for a while an upsurge of population and the establishment of numerous buildings made of bricks and wood. At its height in the 18th century, the fort had twenty cannons and hosted one church and two convents. The decline in importance of Mancera Island in the fort system meant that by 1820, when 