1. On September 23, 1779, the Continental Army, under the leadership of General John Sullivan, defeated the British and their Native American allies in the Battle of Newtown, located in present-day Chemung County, New York. The victory helped secure the Continental Army's hold on the region and facilitated further military operations against the British and their Native American allies.

2. On September 23, 1893, one of the earliest recorded instances of a mass shooting in American history occurred in New Castle, Pennsylvania. The perpetrator, William Courtright, killed four people and wounded several others before being subdued by a group of local men. The incident highlighted the need for stricter laws governing firearms ownership and also fueled debates over the role of mental illness in such tragic events.

3. The Philadelphia Museum of Art opened its doors to the public on September 23, 1928. Designed by American architect Horace Trumbauer, the museum is home to over 240,000 objects, including art from the United States, Europe, Asia, and the Middle East. It is also known for its distinctive steps, which were featured prominently in the classic 1976 film Rocky.

4. On September 23, 1985, a bomb was dropped by the radical group MOVE on a residential building in Philadelphia, killing 11 people and injuring dozens more. The incident sparked a violent confrontation between the group and law enforcement officials, and prompted a national discussion about race, law enforcement, and domestic terrorism.

5. The Pennsylvania State Capitol Building in Harrisburg was dedicated on September 23, 1906. Designed by American architect Joseph Miller Huston, the building features Renaissance Revival-style architecture and is home to the offices of the Governor of Pennsylvania, the Pennsylvania General Assembly, and several state agencies. It is also noted for its impressive dome, which rises 272 feet above street level.