Independence Hall has welcomed visitors for nearly 300 years, first as the Pennsylvania State House and now as a historic site, and preserving the iconic structure has been a challenging and ongoing process. In the 1960s, the National Park Service added steel beams to strengthen the building, and the addition of modern heating, cooling, and fire suppression systems also helped preserve it. Preservation also extends to the Liberty Bell, a powerful symbol of freedom to people around the world, which was long displayed inside Independence Hall. To accommodate increasing crowds, the bell moved to its own building on Independence Mall in 1976 and again in 2003 to its current location.