But if my forces
are not enough, I am hardly the one to relent,
I’ll plead for the help I need, wherever it may be —
If I cannot sway the heavens, I’ll wake the powers of hell!

[Quod si mea numina non sunt
magna satis, dubitem haud equidem implorare quod usquam est:
flectere si nequeo superos, Acheronta movebo.]

Virgil (70-19 BC) Roman poet [b. Publius Vergilius Maro; also Vergil]

The Aeneid [Ænē̆is], Book 7, l. 310ff (7.310-312) [Juno] (29-19 BC) [tr. Fagles (2006)]
    (Source)

(Source (Latin)). Alternate translations:

But if my own power not sufficient be,
Undaunted, aydes I'le seek where ere they dwell;
Will heaven not grant my sute, I'le raise up hell.
[tr. Ogilby (1649)]

If native pow'r prevail not, shall I doubt
To seek for needful succor from without?
If Jove and Heav'n my just desires deny,
Hell shall the pow'r of Heav'n and Jove supply.
[tr. Dryden (1697)]

But if my own divinity is not powerful enough, surely I need not hesitate to implore whatever deity any where subsists: if I cannot move the powers above, I will solicit those of hell.
[tr. Davidson/Buckley (1854)]

If strength like mine be yet too weak,
I care not whose the aid I seek:
What choice 'twixt under and above?
If Heaven be firm, the shades shall move.
[tr. Conington (1866)]

But if not enough my power,
I shall not pause to ask what aid I may.
And if I cannot bend the gods above,
Then Acheron I'll move.
[tr. Cranch (1872), l. 388ff]

If my deity is not great enough, I will not assuredly falter to seek succour where it may be; if the powers of heaven are inflexible, I will stir up Acheron.
[tr. Mackail (1885)]

But if of no avail
My godhead be, I will not spare to pray what is of might,
Since Heaven I move not, needs must I let loose the Nether Night.
[tr. Morris (1900), l. 310ff]

If too weak
Myself, some other godhead will I try,
And Hell shall hear, if Heaven its aid deny.
[tr. Taylor (1907), st. 42, l. 372ff]

If so weak
my own prerogative of godhead be,
let me seek strength in war, come whence it will!
If Heaven I may not move, on Hell I call.
[tr. Williams (1910)]

But if my powers be not strong enough, surely I need not be slow to seek succour wherever it may be; if Heaven I can not bend, then Hell I will arouse!
[tr. Fairclough (1918)]

So, if my power
Falls short of greatness, I must try another’s,
Seek aid where I can find it. If I cannot
Bend Heaven, I can raise Hell.
[tr. Humphries (1951)]

Well, if my powers are not great enough,
I shall not hesitate -- that's sure -- to ask help wherever
Help may be found. If the gods above are no use to me, then I'll
Move all hell.
[tr. Day-Lewis (1952)]

If my power
is not enough, I shall not hesitate
to plead for more, from anywhere; if I
cannot bend High Ones, then I shall move hell.
[tr. Mandelbaum (1971), l. 410ff]

Well, if my powers fall short,
I need not falter over asking help
Wherever help may lie. If I can sway
No heavenly hearts I'll rouse the world below.
[tr. Fitzgerald (1981), l. 423ff]

But if my own resources as a goddess are not enough, I am not the one to hesitate. I shall appeal to whatever powers there are. If I cannot prevail upon the gods above, I shall move hell.
[tr. West (1990)]

But if my divine strength is not
enough, I won’t hesitate to seek help wherever it might be:
if I cannot sway the gods, I’ll stir the Acheron.
[tr. Kline (2002)]

But if my powers
Are not great enough, why should I hesitate
To seek help from any source whatever?
If I cannot sway Heaven, I will awaken Hell!
[tr. Lombardo (2005)]

If I cannot bend the gods, I will move Acheron.
[tr. @sentantiq (2012)]

If my powers aren't enough, why not stoop to begging anyone? If I can't move the gods above, then I'll move Acheron.
[tr. Bartsch (2021)]

If I cannot bend Heaven, I shall move Hell.
[Bartlett's]