Can anyone recommend a serious historical yaoi? Something like Sakura Gari. Or something like Savage Garden (it's not yaoi or shounen ai but there are enough undertones to satisfy me).

I'd appreciate anyone who can help.

Hi Izuru Tokoro no Tenshi, I guess. It's shounen-ai, though, not yaoi. A tragedy and unrequited, too, but then again it's the first title that came to mind when you mentioned serious historical BL, since most BL just use the historical setting as a gimmick.

Ludwig II Sei
Kaze to Ki no Uta
Lueduo Diren De Xin
Coponicus no Kokyuu - Is the 1970s considered historical? If so, then this.

Cantarella - Unrequited, again. But - unusually for this type of story - it actually involves the protagonist, who's in love with both his best friend and his sister, who fall for each other and betray him.

Thomas no Shinzou, So wa Reirei no Yuki ni Mai - Shounen-ai, again.

Yuuutsu na Asa is serious, but I wouldn't call it "dark," compared to the others I've mentioned here. No one dies or kills themselves, at least >_<

These are set in historical era of sorts and have some dark elements:

• Maiden Rose and other works from Inariya Fusanosuke-sensei; Giglio, Zion no Koeda, Shoukei and Rakuen no Izumi
• Tsukigasa (Samurai era?)

I second on Ludwig II Sei (Dropped this one halfway since it got so confusing towards the end ;w; )