Over a field of characteristic zero, a family of polynomials $(p_n)$ is computed by matrix-symmetric circuits of polynomial orbit size if, and only if, there is a constant $k$ such that every $p_n$ is a linear combination of homomorphism polynomials $\hom_{F,n}$ of patterns $F$ of treewidth at most $k$. This is the main result of Dawar, Pago, and Seppelt (ITCS 2026). It follows from the characterisation of bounded-depth matrix-symmetric circuits, as every circuit has finite support depth and every tree decomposition has finite depth.