Taipei, Aug. 7 (CNA) The Danjiang Bridge in northern Taiwan was closed for the first time Thursday for a defensive blockade drill, with troops setting up obstacles to extend the Tamsui River defensive line and prevent enemy forces from advancing toward Taipei. Once the drill began, dump trucks, military vehicles and requisitioned civilian trailers transported blockade materials onto the southbound lanes. Military personnel set up a blockade using concrete blocks, steel hedgehogs, barbed wire and U.S.-made HESCO bastions on the Danjiang Bridge in New Taipei on late Thursday. Sappers climb over the railing of the Danjiang Bridge during a defensive blockade drill in New Taipei late Thursday. The source said the Tamsui River estuary and Bali have long been important defensive positions but were relatively isolated from each other.