As one of the greatest astronomical spectacles, total solar eclipses have long been a subject of scientific interest and have been recorded by numerous civilizations over the millennia. These records are an essential reference for constraining and reconstructing Earth's variable rotation (Delta T) prior to the 17th century. However, Delta T reconstructions for the 4th-7th centuries have significant uncertainties, mainly owing to a data scarcity. Here, we analyze Byzantine historical sources with reports of total solar eclipses along the Eastern Mediterranean coasts and add probable Delta T constraints on their basis. We examined five cases of total solar eclipses in 346, 418, 484, 601, and 693 CE, identified times and locations of the observations, and compared them with the existing Delta T spline curve to derive new Delta T constraints. Our results probably tighten Delta T variability in 346 CE, show a larger Delta T range in 418 CE, and give smaller Delta T ranges in 484, 601, and 693 CE. Our study tightens the existing Delta T variations and occasionally support some Delta T constraints that slightly depart from the Delta T spline curve in the latest reconstructions. Our results are consistent with contemporary Delta T constraints from other studies and offer an improved understanding of Earth's variable rotation.
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