Ultra-large arc-like structures such as the Giant Arc and related features span several billion light-years and appear as coherent crescent or ring-like arrangements of galaxies, gas, and dust, seemingly exceeding the maximum size of structures allowed by the cosmological principle and standard ΛCDM expectations for large-scale homogeneity and isotropy (Lopez et al. 2021; Peebles 2022). These arcs are large and regular enough that it is debated whether they can be genuine matter concentrations or must instead arise from projection effects, selection biases, or dust-related systematics in absorption-based surveys, posing a challenge to ΛCDM either way: as real objects they violate expected size limits, and as artefacts they reveal unmodeled observational biases (Lopez et al. 2024; Nadathur 2023).