Read this: Several churches and monasteries were built inside, or close to, the city of Utrecht. The most dominant of these was the Cathedral of Saint Martin, inside the old Roman fortress. The construction of the present Gothic building was begun in 1254 after an earlier romanesque construction had been badly damaged by fire. The choir and transept were finished from 1320 and were followed then by the ambitious Dom tower. The last part to be constructed was the central nave, from 1420. By that time, however, the age of the great cathedrals had come to an end and declining finances prevented the ambitious project from being finished, the construction of the central nave being suspended before the planned flying buttresses could be finished. Besides the cathedral there were four collegiate churches in Utrecht: St. Salvator's Church (demolished in the 16th century), on the Dom square, dating back to the early 8th century. Saint John (Janskerk), originating in 1040; Saint Peter, building started in 1039 and Saint Mary's church building started around 1090 (demolished in the early 19th century, cloister survives). Besides these churches the city housed St. Paul's Abbey, the 15th-century beguinage of St. Nicholas, and a 14th-century chapter house of the Teutonic Knights.

When was construction completed on the Cathedral of Saint Martin?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable