Nowadays, 1,000,000 is noted in Roman numerals by an M with a line under it. However, it used to be marked by an M with a line above it.
The line over the M signified multiplying the number by 1,000. The letter M represents 1,000, so incorporating a multiplier of 1,000 gave a value of 1,000,000. The Romans rarely had the need to represent numbers this high, so they did not have a special symbol or word for 1,000,000.
The switch from using the line over the M to the one under the M is a recent change. Most computer fonts do not have a ready means to add a line above a letter, so typesets have shifted to the underlined version for ease of display.
Roman numerals are from 110  I, II, III, IV, V, VI, VII, VIII, IX, X. L = 50, C = 100, D = 500, M = 1000. A letter can be repeated only three times. You can find more information
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Larger numbers were indicated by putting a horizontal line over them, which meant to multiply the number by 1,000. It would be C with a line over top.
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The Roman numeral for 755 is DCCLV.
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(225) Two Hundred Twenty five. Improved answer: CCL = 250.
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