Laudator Temporis Acti

Solon, fragment 9 (tr. M.L. West):

As from the cloudbank comes the storm of snow or hail,
    and thunder follows from the lightning flash,
exalted men portend the city's death: the folk
    in innocence fall slave to tyranny.
Raise them too high, and it's not easy afterwards        5
    to hold them. Now's the time to read the signs.

Or, somewhat more literally:

From a cloud comes force of snow or hail,
    and thunder is produced from bright lightning;
from powerful men comes a city's destruction, and through stupidity
    citizens have fallen into bondage to a tyrant.
If someone is raised up too high, it isn't easy to restrain him        5
    afterwards, but right now you need to ponder all that is good.

The Greek:

ἐκ νεφέλης πέλεται χιόνος μένος ἠδὲ χαλάζης,
    βροντὴ δ᾿ ἐκ λαμπρῆς γίγνεται ἀστεροπῆς·
ἀνδρῶν δ᾿ ἐκ μεγάλων πόλις ὄλλυται, ἐς δὲ μονάρχου
    δῆμος ἀϊδρίῃ δουλοσύνην ἔπεσεν.
λίην δ᾿ ἐξάραντ᾿ <οὐ> ῥᾴδιόν ἐστι κατασχεῖν        5
    ὕστερον, ἀλλ᾿ ἤδη χρή <καλὰ> πάντα νοεῖν.

3 ἐς plerique: ἐκ Diodorus Siculus 9.20.2; μονάρχου plerique: τυράννου Diodorus Siculus 19.1.4
5 οὐ add. Dindorf
6 καλὰ add. West: περὶ Dindorf: τινα Sintenis: τάδε Passow

See Maria Noussia-Fantuzzi, Solon the Athenian, the Poetic Fragments (Leiden; Brill, 2010), pp. 309-318.