Complex sentence: Later in the same year, in December, Silence 4 was the first national band to sell out at Pavilhão Atlântico, performing to an astonishing 18,000-strong crowd, only 6 months after the release of their first album.
Split into simpler sentences: Later in the same year, in December, Silence 4 was the first national band to sell out. At Pavilhão Atlântico they performed to an astonishing 18,000-strong crowd, only 6 months after the release of their first album.