Complex sentence: Rúmil of Valinor on which Fëanor supposedly based his was known as sarati, but became later also known as "Tengwar of Rúmil".
Split into simpler sentences: Rúmil of Valinor, on which Fëanor supposedly based his own work, was known as sarati. It later became known as "Tengwar of Rúmil".