Assertion: altar's step | /r/HasProperty | taken by his successor
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Source sentences:
text: This final step was only taken by his successor Attalus I, after he defeated the Galatians in 238, whom Pergamon had paid tribute to under Eumenes I. Only at this point did an entirely independent Pergamene kingdom come into existence, which would reach its greatest power and territorial extent in 188 BC.