for at least 200 years. Earthquake survival At least four strong earthquakes have hit the region since 1280, but the apparently vulnerable tower survived. The reason was not understood until a research group of 16 engineers investigated. The researchers concluded that the tower was able to withstand the tremors because of dynamic soil-structure interaction (DSSI): the height and stiffness of the tower, together with the softness of the foundation soil, influences the vibrational characteristics of the structure in such a way that the tower does not resonate with earthquake ground motion. The same soft soil that caused the leaning and brought the tower to the verge of collapse helped it survive. Technical information Elevation of Piazza del Duomo: about 2 metres (6 feet, DMS) Height from the ground floor: , 8 stories Height from the foundation floor: Outer diameter of base: Inner diameter of base: Angle of slant: 3.97 degrees or from the vertical Weight: Thickness of walls at the base: Total number of bells: 7, tuned to musical scale, clockwise: 1st bell: L'Assunta, cast in 1654 by Giovanni Pietro Orlandi, weight 2nd bell: Il Crocifisso, cast in 1572 by Vincenzo Possenti, weight 3rd bell: San Ranieri, cast in 1719–1721 by Giovanni Andrea Moreni, weight 4th bell: La Terza (1st small one), cast in 1473, weight 5th bell: La Pasquereccia or La Giustizia, cast in 1262 by Lotteringo, weight 6th bell: Il Vespruccio (2nd small one), cast in the 14th century and again in 1501 by Nicola di Jacopo, weight 7th bell: Dal Pozzo, cast in 1606 and again in 2004, weight Number of steps to the top: 296 About the 5th bell: The name Pasquareccia comes from Easter, because it used to ring on Easter day. However, this bell is older than the bell-chamber itself, and comes from the tower Vergata in Palazzo Pretorio in Pisa, where it was called La Giustizia (The Justice). The bell was tolled to announce executions of criminals and traitors, including Count Ugolino in 1289. A new bell was installed in the bell tower at the end of the 18th century to replace the broken Pasquareccia. The circular shape and great height of the campanile were unusual for their time, and the crowning belfry is stylistically distinct from the rest of the construction. This belfry incorporates a correction for the inclined axis below. The siting of the campanile within the Piazza del Duomo diverges