The origin of Diablo

Over a hundred years ago, Tarahia sealed Baal, the Lord of Destruction, with her own body, to prevent him from being disturbed,
Tyrael led members of the Horadrim in building seven tombs for him in the Aranoke desert outside Rugoin,
Only one of them is true. Diablo, after his release, rushes from Tristram to Lugoyne to rescue his brother Baal, and more importantly,
He starts several weeks before the main characters. To stop Diablo,
We had to find tarahia's tomb before he could, but the desert was so vast that even Deckard Kane didn't know where it was,
He only knows to use the Horadric scepter to open the tomb door, the scepter needs to use the Horadric square to synthesize, the protagonist had to clear the demons outside the city first...