Complex sentence: According to "Guangxu Shuntianfu Zhi", heavy rainstorms in Beijing in 1695 flooded the gates at Xuanwumen, making them impossible to open.
Split into simpler sentences: According to "Guangxu Shuntianfu Zhi", there were heavy rainstorms in Beijing in 1695. Rainwater flooded the gates at Xuanwumen, making them impossible to open.