1. On December 13, 1937, the Great Flood of Pittsburgh occurred. Heavy rains caused the Allegheny, Monongahela, and Ohio Rivers to overflow, resulting in one of the worst floods in the city's history. The flood caused massive damage to buildings, homes, and infrastructure, with over 60,000 people left homeless and a death toll of 69.

2. December 13, 1967, marked the opening of the first indoor mall on the east coast, the Cloverleaf Mall in Hagerstown, Pennsylvania. The mall was a significant landmark in the state's retail history, and its success led to the development of several other indoor shopping centers throughout the region.

3. On December 13, 1927, the first transatlantic telephone call was made from New York to London. The historic call was facilitated by Pennsylvania-born AT&T engineer, Walter Gifford. Gifford played a critical role in the development of the global telecommunications industry, and his legacy is celebrated today in his native Pennsylvania.

4. Pennsylvania's Moravian settlement played a vital role in American history, and on December 13, 1775, the first American Moravian hymnal was published. The book contained 1,778 hymns, many of which are still sung today in Moravian churches across the country.

5. December 13, 1837, saw the opening of the first bank in Pittsburgh, the Bank of Pittsburgh. The bank's founding marked an important milestone in the city's economic development, and over the years, it grew to become one of the most significant financial institutions in the region, helping to fuel the city's growth and prosperity.