Thirty thousand. In Joshua 8:12 we read 5,000, and this must be the true reading. Thirty thousand men could hardly have been posted, without detection, in the ravines around Ai, whereas we are informed by travellers that there would have been no difficulty in concealing 5,000 men there.
See, however, the passage cited from Lieut. Conder's Report in the note on Joshua 7:2. The confused condition of the numbers in the present text of the Old Testament is a well known fact, and it is proved by the great discrepancies in this respect between the Books of Chronicles and those of Samuel and Kings.
Some have thought (e.g; Haverniek, 'Introduction to the Old Testament,' II. Joshua 1:15) that two bands were laid in ambush, one on the northwest and the other on the southwest. This is a possible, though not probable, solution of the difficulty (see below).
Then we must suppose that the city was nearly surrounded, Joshua and the main body on the southeast, the larger detachment on the north (verse 13), and the smaller ambush on the west (see note on verse 13).
Keil, in his earlier editions, supposed that Joshua assaulted Ai with 30,000 men, out of whom he chose 5,000 as an ambush. So also Hengstenberg's 'Geschichte des Reiches Gottes,' p. 219. But this only introduces a third contradiction, for we are told both in verses 1 and 3 that Joshua took with him "all the men of war."
Keil has, however, abandoned that supposition, which is contrary to all the ancient versions, including the present text of the LXX. The Bishop of Lincoln suggests that 5,000 men may have been detached to reinforce the former detachment of 30,000.
But to say nothing of the improbability of an ambush of 35,000 men remaining undetected (and they were specially instructed—see next verse—not to station themselves far from the city), we have the plain statement in verse 12 וַיָּשֶׂם אוֹתָם אוֹרֵב "he stationed (or had stationed) them as an ambush."