Ubaldini Migliorino (active 1548), known also as "Captain Mellerin," was an Italian military engineer working in Scotland. He designed new fortifications at the entrances of Edinburgh Castle, Dunbar Castle, and possibly the walled town of Leith.

During the war with England known as the Rough Wooing, on 5 February 1548 Regent Arran appointed Migliorino Ubaldini as supreme commander of all Scottish forces by land and sea. Ubaldini had been sent to Scotland by Henry II of France who called him a famous captain. Despite this, Marcus Merriman, a modern historian, found no recorded details of his previous career. Merriman linked Ubaldini's appointment in Scotland with Lord Methven's plea to Mary of Guise in December 1547 for a French captain who had intelligence to assiege and order artillery.

Two letters written by Ubaldini in 1548 to Mary of Guise survive. In 1548/9 he wrote two letters to the brother of Mary of Guise, the Duc d'Aumale, which note a French form of his name as; "Captain Mellerin." Ulbaldini and Piero Strozzi directed a refortification of Dunbar Castle in September 1548.

At the same period, there was another Ubaldini in Scotland; Petruccio Ubaldini, who fought for English at Haddington. Other Italian engineers who worked in Scotland for the Scottish side during the Rough Wooings include Leone Strozzi, Piero Strozzi, and perhaps Giovanni Portinari, who Nicolas Throckmorton later recruited for English service because he already spoke Scots. Camillo Marini, younger brother of Girolamo Marini, worked on border fortifications at Jedburgh, and at Eyemouth and probably Dunbar Castle in 1550 and 1551. Lorenzo Pomarelli worked for Mary of Guise for six years 1554 - 1560.

Master John Hamilton of Milnburn began building a rampart and blockhouse in February 1547, recorded as casting the "foussys" or ditches on Castle Hill, and reported by James Stewart of Cardonald.

While the English were fortifying Haddington, in March 1548 Ubaldini was working to strengthen Edinburgh Castle. A lodging was found in the Royal Mile for the "Italiane devisar of the forte of the castle hill"." Ubaldini commenced the construction of a renaissance style trace italienne fortification in front of the castle on the present esplanade. Some of the timber and stone used was obtained from the woods and house of Alexander Crichton of Brunstane who had sided with England. His friend and ally Ninian Cockburn vowed the new work would never be finished, writing, "yon neu blak hous quhilk will nocht cum abof the erde."

An account for building the new fort at Edinburgh Castle from January 1547 to 19 July 1550 amounts to £6,377 Scots. There had been a French contribution of at least £4070 Scots for the work.

The triangular blockhouse became known as the Spur. The Imperial envoy Mathieu Strick noted in July 1551 that the completed Spur was decorated with the arms of France. Ubaldini went on to design works at Dunbar Castle in September which were demolished in 1567, and perhaps at Stirling Castle where there are remains of a similar work, called the 'French Spur,' with carved French insignia.