None of these charts is graduated, and the horizontal and
vertical lines which cross many of them represent neither
parallels nor meridians. Their most characteristic feature, and
one by which they can most readily be recognized, is presented
by groups or systems of rhumb-lines, each group of these lines
radiating from a common centre,
the central group being generally
encircled by eight or sixteen satellite
groups. In the course of time
the centres of radiation of all these
groups had imposed upon them
ornate rose dei venti, or windroses,
such as may still be seen upon our
compass-cards. Each chart was furnished
with a scale of miles. These
miles, however, were not the ordinary
Roman miles of 1000 paces or
5000 ft., but smaller miles of Greek
or Oriental origin, of which six were
equal to five Roman miles, and as
the latter were equal to 1480 metres,
the Portolano miles had a length of
only 1233 metres, and 75.2 of the
former, and 90.3 of the latter were
equal to a degree. The difference
between these miles was known,
however, only to the more learned
among the map-makers, and when
the charts were extended to the
Atlantic seaboard the two were
assumed to be identical.
 |
| Fig. 21.—Map illustrating Marino Sanuto’s Liber secretorum fidelium crucis. |
On these old charts the Mediterranean is delineated with surprising fidelity. The meridian distance between the Straits of Gibraltar and Beirut in Syria amounts upon them to about 3000 Portolano miles, equal in lat. 36° N. to 40.9°, as compared with an actual difference of 41.2°, and a difference of 61° assumed by Ptolemy. There exists, however, a serious error of orientation, due, according to Professor H. Wagner, to the inexperience of the cartographers who first combined the charts of the separate basins of the Mediterranean so as to produce a chart of the whole. This accounts for Gibraltar and Alexandria being shown as lying due east and west of each other, although there is a difference of 5° of latitude between them, a fact known long before Ptolemy.
The production of these charts employed numerous licensed draughtsmen in the principal seaports of Italy and Catalonia, and among seamen these MS. charts remained popular long after the productions of the printing-press had become available. The oldest of these maps which have been preserved, the so-called “Pisan chart,” which belongs probably to the middle of the 13th century, and a set of eight charts, known by the name of its former owner, the Cavaliere Tamar Luxoro, of somewhat later date, are both the work of Genoese artists. Among more eminent Genoese cartographers are Joannes da Carignano (d. 1344), Petrus Vesconte, who worked in 1311 and 1327, and is the draughtsman of the maps illustrating Marino Sanuto’s Liber secretorum fidelium crucis, which was to have roused Christendom to engage in another crusade (figs. 19 and 21) Battista Beccario (1426, 1435) and Bartolomeo Pareto (1455). Venice ranks next to Genoa as a centre of cartographic activity. Associated with it are Francesco Pizigano (1367–1373), Francesco de Cesanis (1421), Giacomo Giroldi (1422–1446), Andrea Bianco (1436–1448) Giovanni Leardo (1442–1452), Alvise Cadamosto, who was associated with the Portuguese explorers on the west coast of Africa (1454–1456) and whose Portolano was printed at Venice in 1490, and Fra Mauro (1457).
Associated with Ancona are Grazioso Benincasa and his son Andreas, whose numerous charts were produced between 1461 and 1508, and Count Ortomano Freducci (1497–1538).
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| Fig. 22.—Fra Mauro (1457). |
The earliest among Majorcan and Catalonian cartographers is Angelino Dulcert (1325–1339) whom A. Managhi claims as a Genoese, whose true name according to him was Angelino Dalorto.
