The "altars" of this verse seem to be the same with those of 2 Kings 21:5, and consequently were not in the temple building, but in the outer and inner courts.

Built altars - He placed idolatrous altars even in the temple.

And he built altars in the house of the Lord,.... In the holy place, as distinct from the courts in the next verse; and these were sacred to the idols of the Gentiles:

of which the Lord said, in Jerusalem will I put my name; in the temple there, devoted to his service, called by his name, and where his name was called upon, see Deuteronomy 12:5 and to erect altars to idols here must be very abominable to him.

And he built altars in the house of the LORD, of which the LORD said, In Jerusalem will I put my name.

21:1-9 Young persons generally desire to become their own masters, and to have early possession of riches and power. But this, for the most part, ruins their future comfort, and causes mischief to others. It is much happier when young persons are sheltered under the care of parents or guardians, till age gives experience and discretion. Though such young persons are less indulged, they will afterwards be thankful. Manasseh wrought much wickedness in the sight of the Lord, as if on purpose to provoke him to anger; he did more evil than the nations whom the Lord destroyed. Manasseh went on from bad to worse, till carried captive to Babylon. The people were ready to comply with his wishes, to obtain his favour and because it suited their depraved inclinations. In the reformation of large bodies, numbers are mere time-servers, and in temptation fall away.