In the fourteenth century, a number of political developments cut Europe's overland trade routes to southern and eastern Asia, with which Europe had had important and highly profitable commercial ties since the twelfth century. This development, coming as it did when the bottom had fallen out of the European economy, provided an impetus to a long-held desire to secure direct relations with the East by establishing a sea trade. Widely reported, if somewhat distrusted, accounts by figures like the famous traveler from Venice, Marco Polo, of the willingness of people in China to trade with Europeans and of the immensity of the wealth to be gained by such contact made the idea irresistible. Possibilities for trade seemed promising, but no hope existed for maintaining the traditional routes over land A new way had to be found.

The chief problem was technological: How were the Europeans to reach the East? Europe's maritime tradition had developed in the context of easily navigable seas—the Mediterranean, the Baltic, and, to a lesser extent, the North Sea between England and the Continent—not of vast oceans. New types of ships were needed, new methods of finding one's way, new techniques for financing so vast a scheme. The sheer scale of the investment it took to begin commercial expansion at sea reflects the immensity of the profits that such East-West trade could create. Spices were the most sought-after commodities. Spices not only dramatically improved the taste of the European diet but also were used to manufacture perfumes and certain medicines. But even high-priced commodities like spices had to be transported in large bulk in order to justify the expense and trouble of sailing around the African continent all the way to India and China.

The principal seagoing ship used throughout the Middle Ages was the galley, a long, low ship fitted with sails but driven primarily by oars. The largest galleys had as many as 50 oarsmen Since they had relatively shallow hulls, they were unstable when driven by sail or when on rough water: hence they were unsuitable for the voyage to the East. Even if they hugged the African coastline, they had little chance of surviving a crossing of the Indian Ocean. Shortly after 1400, shipbuilders began developing a new type of vessel properly designed to operate in rough, open water: the caravel. It had a wider and deeper hull than the galley and hence could carry more cargo: increased stability made it possible to add multiple masts and sails. In the largest caravels, two main masts held large square sails that provided the bulk of the thrust driving the ship forward, while a smaller forward mast held a triangular-shaped sail, called a lateen sail, which could be moved into a variety of positions to maneuver the ship.

The astrolabe had long been the primary instrument for navigation, having been introduced in the eleventh century. It operated by measuring the height of the Sun and the fixed stars: by calculating the angles created by these points, it determined the degree of latitude at which one stood (The problem of determining longitude, though, was not solved until the eighteenth century.) By the early thirteenth century. Western Europeans had also developed and put into use the magnetic compass, which helped when clouds obliterated both the Sun and the stars. Also beginning in the thirteenth century, there were new maps refined by precise calculations and the reports of sailors that made it possible to trace one's path with reasonable accuracy. Certain institutional and practical norms had become established as well.

A maritime code known as the Consulate of the Sea, which originated in the western Mediterranean region in the fourteenth century, won acceptance by a majority of sea goers as the normative code for maritime conduct; it defined such matters as the authority of a ship's officers, protocols of command, pay structures, the rights of sailors, and the rules of engagement when ships met one another on the sea-lanes. Thus by about 1400 the key elements were in place to enable Europe to begin its seaward adventure.

自12世纪起，欧洲就已经建立起与南亚和东亚之间高度互利的贸易关系，但14世纪时，政治的发展切断了双方的陆路贸易路线。政治的发展在将欧洲经济带入谷底的同时，也提供了一个新契机，通过建立一个欧洲与东方的海上航路确保两者之间直接的贸易往来，实现长久以来的愿景。

对此有诸多报道，有些可能不足为信，威尼斯著名旅行家马可•波罗在其书中就描述了中国人希望和欧洲人通商的意愿，认为通过贸易关系欧洲可以获得巨额财富，他的这些描述让欧洲人难以抗拒。双方贸易有无限商机，前景看好，但传统的陆路贸易已然无望，所以开辟新的贸易路线势在必行。

技术问题最为重要：欧洲人如何到达东方？欧洲的航海传统是在那些易于航行的海域中建立和发展起来的——地中海、波罗的海，以及一条比较狭长的海域，英格兰和欧洲大陆之间的北海，而这些都并非广阔的海洋。因此，开辟新的航线就需要新型的轮船、新的导航技术，以及支持这一庞大计划的新的融资技术。开启海上商业扩张投入的资金规模反映出东西方贸易所能创造出的巨大财富。香料在当时成为最受欢迎的商品，不仅显著提高了欧洲菜肴的口感，同时也被用于制作香水和一些药品。但即使是香料这样的高价商品也不得不大批量运输，以平衡绕行非洲运输至中国和印度所耗费的巨额成本和麻烦。

中世纪应用最为广泛的海船是划桨帆船，船体低矮狭长能够使用帆，但主要还是靠浆操控。最大的划桨帆船有50个划手由于船体相对较浅，靠帆航行或是在汹涌的海面上航行时很难保持稳定。因此它们不适合在去往东方的航线上航行。即使紧贴着非洲海岸线行驶，这种船也很难穿越印度洋。15世纪初，造船专家们开始研制一种能够适用于波涛汹涌的开放海域的新型船只——轻快帆船。这种海船船体比划桨帆船更宽更深，因此可以运送更多的货物，稳定性的提升使得船体能够增加多个桅杆和船帆。最大型的轻快帆船上，两根主桅杆撑起大块船帆就能够提供足够的推力驱动帆船前进，同时一个小型的前桅杆撑起一块三角形船帆，这种船帆叫做三角帆，它可以移动到不同位置控制帆船。

自11世纪星盘引入欧洲以来，它已经成为航海的重要工具。星盘通过测定太阳和恒星的高度来计算罗盘与星体之间的夹角，并以此确定测量者所处的纬度（而经度测量的难题，直到18世纪才得以解决）。13世纪初，西欧人也发明并开始使用磁罗盘，在云彩遮挡住太阳和星星的情况下帮助他们辨识方向。也是在13世纪初期，经过精密计算，绘制的地图更为精准，加上航海日志，使航行变得可靠而准确。航海制度和实际规范也日趋完善。

14世纪，一部起源于地中海西部地区的《海运法典》为大多数水手们所接受，成为海事行为的规范标准。法典规定了船长的职权范围、命令协议、薪酬结构、水手们的权利，以及航行中与其他船只的交战规则。因此，直到大约1400年，正是这些重要的因素的具备，欧洲人才能够开启他们的海上冒险之旅。

(旧时常由奴隶或犯人划桨的) 划桨帆船
三角形的船帆，最早是由阿拉伯人发明，通常用斜三角帆，大型阿拉伯三角帆船的主帆远大於後桅帆，船首呈尖形，船尾有的开有窗户，并加装饰。