Let me explain
Each of the 7 piers stands on a 3 to 6 metre thick footing over 4 shafts 9 to 18 metres deep. The piers, 77 to 245 metres tall, rose 4 metres every 3 days and split into two legs 90 metres below the deck to keep the bridge flexible. The 36,000-tonne steel deck was assembled on land behind both abutments and pushed out over the piers by 64 hydraulic launchers at about 9 metres an hour; the two halves met on 28 May 2004, 270 metres above the Tarn. The first stone was laid on 14 December 2001, the viaduct was inaugurated on 14 December 2004 and opened to traffic on 16 December 2004 (official Millau Viaduct website).