Faithful propagation of genomic material during the cell division cycle is crucial for the cells of our body to keep malignancy in check and ageing at bay. Cells prepare our DNA for division by packing it tightly into highly condensed and resolved chromosomes. Chromosomes that are not correctly folded cause major problems in mitosis and lead to genome instability through bridging or chromosome loss during anaphase. Maintaining chromosomes in a compacted disentangled state before division is therefore essential, yet, the process of chromosome maintenance is poorly understood. Topoisomerase 2A (TOP2A), a DNA metabolising enzyme commonly targeted by chemotherapy for cancer, is known to be involved in shaping and disentanglement of chromosomes. Previous studies have suggested a role in the establishment of mitotic chromosome structure. A major difficulty with studying TOP2A in mitosis is that it has key functions in transcription and DNA replication. Therefore systems such as RNAi that deplete protein over multiple cell cycles make it difficult to define primary phenotypes. To precisely pinpoint the function of TOP2A in mitosis we have engineered a human cell line that is capable of ultra-rapid conditional TOP2A depletion using the novel auxin/degron system. TOP2A depletion causes chromosome bridging and cells arrest before cytokinesis. Within 30 minutes of depletion of TOP2A, chromosomes in mitosis begin to untangle and lose structure. Correspondingly, when TOP2A is rapidly removed from cells arrested in prometaphase overnight with hypercondensed chromosomes, the chromosomes unravel and appear to twist and re-entangle. Our novel data argue that TOP2A has a key role in the maintenance of mitotic chromosome compaction and suggest paradoxically that the enzyme is a key structural component of mitotic chromosomes.