Albert Barnes Commentary 2 Kings 18:17

"And the king of Assyria sent Tartan and Rab-saris and Rabshakeh from Lachish to king Hezekiah with a great army unto Jerusalem. And they went up and came to Jerusalem. And when they were come up, they came and stood by the conduit of the upper pool, which is in the highway of the fuller`s field." — 2 Kings 18:17 (ASV)

An interval of time must be understood between this verse and the previous one. Sennacherib, content with his successes, had returned to Nineveh with his plunder and his many captives. Left to himself, Hezekiah regretted his submission and began negotiations with Egypt (2 Kings 18:21, 24; Isaiah 30:2–6; Isaiah 31:1), which implied treason against his Assyrian overlord. It was under these circumstances that Sennacherib appears to have made his second expedition into Palestine very soon after the first.

Following the usual coastal route, he passed through Philistia on his way to Egypt, leaving Jerusalem to one side. He despised such an insignificant state and knew that the submission of Egypt would also secure the submission of its allies. While besieging Lachish on his way to face his main enemy, however, he decided to test the resolve of the Jews by sending an embassy.

Tartan and Rabsaris and Rab-shakeh — None of these are proper names. “Tartan” was the standard title of an Assyrian general; “Rab-saris” means “chief eunuch,” always a high officer of the Assyrian court; and “Rab-shakeh” is probably “chief cup-bearer.”

By the conduit of the upper pool — This was possibly a conduit on the north side of the city near the “camp of the Assyrians.” The location was the same one where Isaiah had met Ahaz (Isaiah 7:3).