Why did Guglielmo Marconi use a vertical aerial in his radio experiments?

Guglielmo Marconi utilized a vertical aerial in his early radio experiments primarily to increase the range of his signaling.1

By connecting one side of his spark gap to an elevated wire—essentially an antenna—and the other to the Earth, he was able to systematically improve the distance over which he could transmit signals. This configuration, often featuring a metal plate or cylinder at the top of a pole, allowed him to extend his transmission range to approximately 2.4 km (1.5 miles) during his initial tests at his father's estate. This success was a pivotal moment that convinced Marconi of the practical potential of wireless communication, leading him to further refine his apparatus by using balloons and kites to achieve even greater heights for his aerials in subsequent demonstrations.21