An attempt to outflank Lee from the south failed under Butler, who was trapped inside the Bermuda Hundred river bend. Each battle resulted in setbacks for the Union that mirrored those they had suffered under prior generals, though unlike them, Grant chose to fight on rather than retreat. Grant was tenacious and kept pressing Lee's Army of Northern Virginia back to Richmond. While Lee was preparing for an attack on Richmond, Grant unexpectedly turned south to cross the James River and began the protracted Siege of Petersburg, where the two armies engaged in trench warfare for over nine months.