They are usually referred to by number:
# Symphony. no.1, C, op.21 (1800)
# Symphony. no.2, D, op.36 (1802)
# Symphony. no.3, 'Eroica', E♭, op.55 (1803)
# Symphony. no.4, B♭, op.60 (1806)
# Symphony. no.5, c, op.67 (1808)
# Symphony. no.6, 'Pastoral', F, op.68 (1808)
# Symphony. no.7, A, op.92 (1812)
# Symphony. no.8, F, op.93 (1812)
# Symphony. no.9, 'Choral', d, op.125 (1824)