With the caveat that I'm not an expert, that's the pommel (hilt is the entire handle) and it is at the bottom to prevent the sword from slipping out of your hand.

https://en.wikipedia.org/wiki/Hilt

Heh, you're right on both counts; thanks! Looks like the pommel at the end acts as a counterweight for heavy swords.

Yeah, think about how leverage works, those things really suck to swing around and manipulate if you just bang them out without consideration for balance. Especially the larger ones...