Cell division is fundamental for cellular duplication. In simple cells like Escherichia coli bacteria, the actin homolog FtsA is essential for cell division and assembles into a variety of protein filaments at the cytoplasmic membrane. These filaments help to tether polymers of the tubulin-like FtsZ to the membrane at early stages of cell division, but also play crucial roles in recruiting other cell division proteins to a complex called the divisome. Once assembled, the E. coli divisome subsequently activates synthesis of the division septum that splits the cell in two. One recently discovered oligomeric conformation of FtsA is an antiparallel double stranded filament. Using a combination of in vivo crosslinking and genetics, we provide evidence suggesting that these FtsA double filaments have a crucial role in activating the septum synthesis enzymes.