Nothing lasts forever, few things even last for long: all are susceptible of decay in one way or another; moreover all that begins also ends.
Nihil perpetuum, pauca diuturna sunt; aliud alio modo fragile est, rerum exitus variantur, ceterum quicquid coepit et desinit.
Original text (Latin)
Notes from Wikiquote
From Ad Polybium De Consolatione (Of Consolation, To Polybius), chap. I; translation based on work of Aubrey Stewart