The paper aims to reconstruct peak discharges of historic floods in an urbanized area of the historic city of Prague based on documentary sources from pre-instrumental and the early instrumental period (1481–1825). Approximately 20–30 maximum water levels are denoted by flood-marks, accounts describing or related at unchanged sites, or by early instrumental measurements. The challenge in this reconstruction is the identification and consideration of man-made floodplain modifications influencing the cross-section area and the hydraulic roughness. In order to overcome this problem, a simple approach to estimate peak discharges of historic floods has been developed and applied to the River Vltava. This approach includes a procedure for reconstructing the hydraulic parameters of the river channel and inundated floodplain, coupled with an approach for the verification of estimated peak discharge reliability. As a result of the different hydraulic characteristics associated with ice jam floods all winter-flood events are excluded to avoid their potential inclusion. We present 18 reconstructed discharge maxima. The validation of the technique by comparison with the recent gauged flood of 2002 reveals results of adequate accuracy. The comparison also shows that the flood event of 2002 was conspicuously greater than all calculated summer floods in 1481–1825.