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International audienceWe study congruences of lines $X_\omega$ defined by a sufficiently general choice of an alternating 3-form $\omega$ in $n + 1$ dimensions, as Fano manifolds of index 3 and dimension $n - 1$. These congruences include the $G_2$-variety for $n = 6$ and the variety of reductions of projected $\mathbb{P^2}$ x $ \mathbb{P^2}$ for $n = 7$.We compute the degree of $X_\omega$ as the $n$-th Fine number and study the Hilbert scheme of these congruences proving that the choice of $\omega$ bijectively corresponds to $X_\omega$ except when $n = 5$. The fundamental locus of the congruence is also studied together with its singular locus: these varieties include the Coble cubic for $n = 8$ and the Peskine variety for $n = 9$.The residual congruence $Y$ of $X_\omega$ with respect to a general linear congruence containing $X_\omega$ is analysed in terms of the quadrics containing the linear span of $X_\omega$. We prove that $Y$ is Cohen–Macaulay but non-Gorenstein in codimension 4. We also examine the fundamental locus $G$ of $Y$ of which we determine the singularities and the irreducible components

Fano congruences of index 3 and alternating 3-forms