Learn French: Ces vieux châteaux ont les tours les plus basses. - These old castles have the lowest towers.

In French, when a superlative adjective comes after the noun, you must repeat the definite article (le, la, or les). Literally, it translates to "the towers the most low."

Is tour feminine here? I thought it was masculine.

It depends on the meaning! Un tour (masculine) means a turn, a trick, or a journey (like the Tour de France). Une tour (feminine) means a tower. Since we are talking about castles, it is feminine, which is why the adjective is the feminine plural basses.

How do we get basses from the adjective bas (low)?

To make the masculine adjective bas feminine, you double the final 's' and add an 'e', making it basse. Then, because we are talking about multiple towers, you add an 's' for the plural to get basses.

Why does vieux go before the noun but basses goes after?

Vieux (old) is a common adjective that goes before the noun. Bas (low) describes physical shape and usually goes after the noun. When you turn an adjective into a superlative with les plus, it simply stays in its normal position.