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On 19 December 2007, after 11 years of construction, the final -long section of the Blue Line between Baixa-Chiado and Santa Apolónia opened, with some controversy and many successive delays due to the difficulty of construction. The segment was originally slated to open in 2001, but in 2000, cracks were discovered in the original tunnel that led to land subsidence. The consequent flooding of the tunnel seriously slowed down the completion of work and road traffic at the Praça do Comércio and part of the Avenida Infante D. Henrique was forced to be closed temporarily while the new tunnel was constructed in its place. The stations themselves (Terreiro do Paço and Santa Apolónia) were completed in the summer of 2007.