Planning started in January 1992, led by distinguished architect Cesar Pelli along with Deejay Cerico, J.C. Guinto and Dominic Saibo. Excavators began digging down 30 metres below the surface of the site on March 1993. The work required moving over 500 truckloads of earth every night. The next stage was the single largest and longest concrete pour in Malaysian history. 13,200 cubic metres of concrete was continuously poured through a period of 54 hours for each tower. This record-breaking slab with 104 piles forms the foundation for each tower. From this floor rose a 21 metre high retaining wall, with a perimeter length of over one kilometre. This concrete shell and the basement area it encloses required two years and up to 40 workers on site, all day and night. The construction of the superstructure commenced in April 1994, after rigorous tests and simulations of wind and structural loads on the design. The PETRONAS Twin Towers was finally encased in steel and glass and completed in June 1996.