Bysse's Tower, a semi-circular mural tower, which in this context means a tower built into and projecting from a city wall rather than standing independently, once formed part of the eastern circuit of Dublin's medieval walls. It sat roughly two-thirds of the way up what is now Parliament Street, positioned between Buttevant's Tower to the north and Dames' Gate to the south. It survived long enough to appear on Richard de Gomme's 1673 map of Dublin, but was demolished in 1763 when Parliament Street was laid out as a new civic thoroughfare, cutting straight through the old wall line.

The tower takes its name from the Bysse family, Dublin merchants and gentlemen who held leases on several of the city's wall structures. In 1574, the Dublin Assembly Roll recorded a lease granted to Robert Byce, who agreed to maintain not only this tower but also Buttevant's Tower and the bulwark between them, all for an annual rent of six shillings and eight pence Irish. A detailed survey carried out in 1585 described the structure precisely: a demi-tower of three storeys, with no vault but two timber lofts, five arrow loops across its lower two levels, walls four feet thick, standing twenty-six feet high, and measuring sixteen feet square internally. By 1609, a further agreement in the Assembly Roll shows Christopher Byse securing a ninety-nine-year lease on the same cluster of towers, paying the same modest rent, suggesting the family maintained a long association with this stretch of the city's defences.

Today there is nothing to see above ground. No masonry, no outline, no trace of the wall survives at street level along this stretch. A marker plaque was installed in 2002 to acknowledge the tower's former location, and that small piece of street furniture is the only indication that Parliament Street was once not a street at all, but the line of a medieval fortification. The plaque is worth pausing at, if only to recalibrate the scale of what stood here; a three-storey defensive tower rising eight metres from the ground, overlooking the Liffey approach to the city.