What is "at unaware"

Unawares \Un`a*wares"\, adv. Without design or preparation; suddenly; without premeditation, unexpectedly. ``Mercies lighting unawares.''
--J. H. Newman.

Lest unawares we lose This our high place, our sanctuary, our hill.
--Milton.

At unaware, or At unawares, unexpectedly; by surprise.

He breaks at unawares upon our walks.
--Dryden.

So we met In this old sleepy town an at unaware.
--R. Browning.