A Question of Loyalty

[William Cloud Hicklin]

But why were Sauron's lot there? Perhaps detected by outlooks on the east bank of the Anduin?

Much further back. According to the Chronology, Sauron's agents in Moria (presumably the "black uruks of Mordor") sent bird-messengers to Barad-dur immediately after the Company's escape. Sauron responded by sending out Grishnakh and his force (presumably much larger than 40, originally). Saruman meanwhile did the same. Grishnakh (and the Nazgul) had originally intended to waylay the Company at Sarn Gebir. There was ample time, since the Co. spent a month in Lorien.

Mind you, Sauron did not *know* the Ring was there. It was a reasonable supposition, but S had had no positive fix on the Ring since he learned of the events at Weathertop and the Bruinen (some weeks after the fact).