In 1232, Choe Woo, against the pleas of both King Gojong and many of his senior civil officials, ordered the Royal Court and most of Gaesong's population to be moved from Songdo to Ganghwa Island in the Bay of Gyeonggi, and started the construction of significant defenses to prepare for the Mongol threat. Choe Woo exploited the Mongols' primary weakness, fear of the sea. The government commandeered every available ship and barge to transport supplies and soldiers to Ganghwa Island. The government further ordered the common people to flee the countryside and take shelter in major cities, mountain citadels, or nearby offshore islands. Ganghwa Island itself was a strong defensive fortress. Smaller fortresses were built on the mainland side of the island and a double wall was also built across the ridges of Mt. Munsusan.